Where the River meets the Sea: The Shannon Estuary


River estuaries have a special allure to me. These wide expanses of neither river nor ocean, neither land nor sea have been shaped by the endless rhythm of the tides on one side and the flow of the river on the other. Each low tide reveals an intricate pattern of channels and runnels that have been carved into the vast areas of sand and mud. The largest estuary in Ireland, the Shannon-Fergus Estuarine Complex or simply the Shannon Estuary, is right on my doorstep and even after many years it is an unrivalled experience to simply spend some time down at the river. This understated landscape carries a tranquillity and openness no other place can rival.

Poulnasherry Bay is a wide sheltered inlet that opens between Cappa and Querrin on the northern side of the estuary. It is a calm late summer morning. I have fumbled my way through the darkness along a small boreen and now I sit on the upper shore of the estuary. The black of the night is slowly turning into a blue haze and the outline of the opposite shore only a kilometre or so across the water becomes visible. The landscape is flat, its skyline only interrupted by solitary trees and a few houses and farm sheds. It is quiet apart from the gentle lapping of the tide, the slow coming and going of the water over the sand that exposes a bit more of the shore with every retreat. A dark shape wanders along the waterline, stops for a moment and disappears into the water. The otter’s footprints are being washed away by next gentle wave and it is as it has never been here.

Light levels are slowly rising and with the first purple hue on the horizon the birds of the estuary awaken. The first ones up are usually the oystercatchers that announce themselves with a high pitched, sharp call and seconds later a group of birds zips by, flying close to the surface of the water to find a quiet place for breakfast. The striking colours of the birds, the black and white body and the bright red beak, are however still muted in the twilight and all I can see are dark shapes flying past. At this time of the year the change from night to day is a swift affair and it is getting brighter with every minute. The sun is just below the horizon now and the sky shows a glowing mix of red, orange and yellow. The morning concert of the estuary has begun and the air is filled with chittering, whistling, bubbling and chirping, the most beautiful sounds in the world. The tide has further retreated unveiling a coarse and colourful stretch of sand which is dotted with stones and seaweeds, their still wet surface vibrant in the first light. I hear a harsh croaking sound and a grey heron descends only a few meters away and touches down on the channel the retreating tide has left. The biggest of the estuary birds finds its position and freezes in the hope some fish will swim by in striking distance of his long beak. Now that the sun is rising quickly the concert of the estuary choir comes to an end and for a while it will be quiet before distant car noises mark the start of another working day for the human population along the estuary. I will sit and watch for another while.


The River Shannon emerges in the Cuilcagh Mountains at the border between County Fermanagh and County Cavan. From here the river makes its way almost straight south through Ireland’s midlands, taking on the waters of numerous tributaries and forming several lakes along the way. After some 150 kilometres the now mighty stream turns west towards the city of Limerick and the coast. After winding its way through the city, the Shannon is heading straight west, widens considerably and becomes tidal. This is the start of the Shannon Estuary that stretches for some 100 kilometres before it meets the Atlantic Ocean between Kilcredaun Point on its County Clare side and Kilconley Point in County Kerry. Here the waterway opens even further into the Mouth of the Shannon. This expanse of water is enclosed by sheer cliffs and its entrance is marked by the headlands of Loop Head to the North and Kerry Head to the South. Beyond those headlands lies the open Atlantic Ocean.

The Shannon Estuary is a bit of a paradox. For centuries this waterway has been one of the main routes into Ireland for both passengers and goods as well as an important fishing ground. While local fishery has been in decline for a while, goods are still being brought into Ireland via the Shannon Estuary and unloaded at the deep-water port at Foynes which is one of the biggest in Ireland and handles cargo from all over the world. Not too far away from Foynes, Shannon Airport, one of the major airports of the country, sits on the banks of the estuary. There is also the controversial Aughinish Alumina plant and two coal, oil and gas fired power stations, one at Moneypoint on the Clare side and one in Tarbert on the Kerry side. Those do not only add to the shipping traffic but also pose a constant threat to the fragile habitats of the estuary.

Despite this human presence the Shannon Estuary is one of Ireland’s most intriguing and important sites for wildlife. Birds are the most apparent inhabitants of the estuary. The sheer cliffs around the Mouth of the Shannon are breeding sites for fulmars, kittiwakes, guillemots and razorbills that arrive in their hundreds in early spring, turning the coast into a cacophony of cackling, growling, whistling and twittering. One reason for these birds to choose the Mouth of the Shannon as their nesting site is the rich food supply. Especially herring and sprat are abundant, and these not only attract the local nesting population but also animals from further afield. Gannets have their nesting site on the Skellig Islands some 100 kilometre south but are a common sight at the lower estuary during the summer. The shores of the estuary are also home to some permanent residents. Cormorants and shags along with herring gull, lesser black backed gull and great black backed gull still appear in high numbers while rarer species like the chough, unmistakable with its red beak and legs, and the raven, whose wonderfully eerie croak has become a rare sound in Ireland, have established a stronghold along the Shannon Estuary.

After the summer visitors have reared their offspring and have left the cliffs in a sprinkled black and white pattern, a mix of bare rock and guano, they return to the open ocean to make space for the winter visitors. The upper estuary features a number of sheltered creeks, inlets and bays most of which reveal wide sandy beaches and vast mudflats once the tide is out. These places are the perfect wintering grounds for waders and waterfowl. Brent goose, whooper swan, lapwing, curlew, greenshank, redshank, ringed and golden plover, knot, dunlin, shelduck, wigeon and others join resident birds like the grey heron, little egret, oystercatcher, snipe and mallard from October onwards.

The creeks, inlets and bays have formed mainly where rivers join the estuary. There are the Glencorbly River at Glin, the White River at Loghill and the Robertstown River and Poulweala Creek at Foynes and Aughinish to name but a few. The main contributary however is the Fergus River that joins the Shannon from the north forming its own vast estuary. Together these two rivers create the largest mudflat in Ireland which is dotted with a number of islands, Deer Island and Coney Island being the largest, that provide undisturbed resting places for the visiting birds.

From a distance the mudflat, this expanses of glorious mud and sand, appears dull and lifeless. A closer look however reveals an abundance of life which to some extend is responsible for the very existence of the mudflat. Mudflats consist of very small sand particles, smaller than the grains found on a sandy beach, that have been moulded together by tidal currents. The electrical charge, that causes repulsion between the grains, is very much reduced in the tiny particles that form the mudflat. This makes them stick together more easily and the inhabitants do the rest by adding mucus and faeces to the mix. The result is a very stable habitat that can resist the action of the tides much better than a sandy beach.

Most of the mudflat community lives underground. Apart from single celled organisms like diatoms (single celled algae), cyanobacteria and flagellates, worms are among the main inhabitants of the mud. The most common sign of their presence are the spaghetti-like castings of the lugworm. This pinkish-reddish and up to 25 centimetre long worm lives in a U-shaped burrow. The head of the worm sits at the bottom of this burrow where it takes in air and sand particles through the so-called feeding funnel. The opening of this funnel is visible on the surface as a small saucer shaped depression usually a few centimetres away from the castings. The worm strips the ingested sand particles from all organic and nutritious material and passes them from its tail end where they appear on the surface as the beforementioned coiled castings. Doing so is always a risk, the tail poking out of the mud might attract unwanted attention and the worm could end up as a tasty snack for an attentive flatfish or the wading birds. The lugworm usually stays in its burrow for weeks or months and only on rare occasions leaves the mud to build a new burrow. Another worm that shows its presence in a more elaborate way is the sand mason. Unlike the lugworm the sand mason builds itself a tube from sand grains and shell fragments that are being glued together by mucus. The top of this tube is visible on the surface of the mudflat and often branches out with finger-like extensions resembling a tiny tree. These branches of course have a function other than being decorative. Below the surface the tube can reach a length of up to 45 centimetres, the worm itself grows to a length of 30 centimetres and retreats to the bottom of the tube at low tide. When the tide is in the worm crawls up and extends his tentacles to catch debris and food and the branches of his sand-tree support it in its efforts by slowing down the flow of the water.

Other inhabitants of the mudflats remain completely invisible. The cockle, razor shell and scallop are all member of the bivalve family, molluscs with two hinged shells. These animals stay buried in the mud or sand and hold themselves in place by a muscular foot that sticks out on one end of the shell. From the other end of their shell they can extend siphons that reach up to the surface. One of those, the inhalant siphon, is used to draw in water which then passes over the feather-like gills of the animal. These gills absorb oxygen and also filter out any food particles. The filtered water is then passed out again through a second syphon, the exhalant siphon. These animals can only breath and feed when the tide is in. Once the tide is out the animal closes the two halves of its shell and retreats further below the surface to get out of the reach of predators. Bivalves are however not completely stationary. Cockles and razor shells especially can move along the surface to escape predators or find a new spot to bury by using their muscular foot and shell movement.

Both the worms and bivalves are a main food source not only for crustaceans like crabs and lobsters and the various fish species of the estuary but also for the waders who are uniquely adapted to search for this kind of food. Birds with long beaks like the oystercatcher are tactile foragers. They actively probe the ground for prey. Birds with shorter beaks like the plovers are visual foragers. They wait for signs of activity and only when they notice movement under the surface the go in. These different feeding methods become obvious in the behaviour and movement of the birds. While the Oystercatcher roams in a rather calm and organized way, probing the ground with every step, plovers are all over the place, running, stopping, looking and running again without any discernible pattern.

On the upper shore where the surface is being covered by the tide only on occasion and where humans haven’t interfered with artificial coastal defences the mudflat has developed into a saltmarsh. These areas are often dominated by the common cord grass. This invasive species is a hybrid between the native small cord grass and the smooth cord grass which was introduced from North America. Initially this hybrid grass with its dense rooting system and thick growth on the surface was very welcome and used to stabilize the coastline. Soon however the common cord grass took matters into its own hands and spread aggressively all along the Irish coast. Today it not only is a threat to the native flora, but the common cord grass also takes over feeding and roosting sites for waders and wildfowl. Where the common cord grass hasn’t invaded yet the native saltmarsh flora, which includes a number of salt tolerating wildflowers, still thrives. Throughout spring and summer, a trio of purple flowering plants add a splash of colour to the landscape of the saltmarsh. It starts in April with thrift, also known as sea pink, which often grows side by side with the less obvious scurvy grass, a small white flowering plant rich in vitamin C which in the past has been used in a pickled form by seafarers. In summer the sea lavender with its delicate tiny flowers appears, followed by the striking sea aster whose yellow and purple flowers turn into fluffy seed heads towards the end of the summer.

The most westerly of the sheltered bays along the Shannon Estuary is also the most unusual one. Rinevella Bay just south of Carrigaholt is divided by a small headland which separates two very different habitats. To the west of the headland lies a wide sandy beach which faces Rehy Hill, the only noteworthy elevation in West Clare. In spring Rehy Hill turns yellow from the flowering gorse shrub that covers most of the hillside and in late summer carpets of heather add a purple hue. The hill is also home to one of the herds of feral goats that roam the Loop Head Peninsula and they can often be seen wandering the sheer cliffs in search for food or resting at sea level side by side with cormorants, shags and gulls. The eastern part of Rinevella Bay is a rare and mesmerizing place. The landward side is known as Clonconneen Marsh or Clonconeen Pool, a narrow stretch of marshland, much of it covered in the infamous common cord grass, with a number of brackish pools. Adjoining this marshland is a shingle barrier that in spring and summer is home to numerous wildflowers. This plant community consists of typical shingle species like orache, sea beat and cushions of sea campion. The rare and poisonous yellow horned poppy is abundant here as well as the also poisonous woody nightshade, also known as bittersweet. This small plant that produces beautiful yellow-purple flowers got its latter name from the at first green and after ripening red berries that apparently offer a bittersweet taste. Unfortunately those berries are also the most poisonous part of the plant. In addition to the wildflowers the stretch of shingle features a number of out of place looking tree trunks. Their presence however becomes clear once the seaward side of the shingle beach comes into view. This bay is known as the Drowned Forest and consists of peat in which countless petrified tree trunks are embedded. Most of the trunks are scots pine but a number of birch branches are also visible in the dark peat. This drowned forest came into being during a sudden change in climate some 4000 years ago. The change from a continental regime to a milder and wetter climate sparked the formation of the vast blanket bogs of the coast and mountains and raised bogs of the midlands. At the coast this event was followed by a rise in sea level and as a consequence many forests were, after first being engulfed by the fast-growing bog, flooded by the sea. At the Shannon Estuary it is evident that this forest once covered a huge area. While the drowned forest at Rinevella is a constant reminder of the past, in other parts of the estuary the peat is covered in sand and mud but makes occasional appearances especially after rough weather. Even further afield, all along Ireland’s west coast, these old forests appear from under beaches and stretches of shingle only to disappear when sand and stones shift again. At Rinevella the peat with its embedded tree trunks is slowly being dismantled by the coming and going of the tides and the shape of this coastline is changing almost on a monthly basis. The remaining and by now rather battered looking peat platforms are one of the main feeding grounds of the Brent geese that spend the winter at the estuary. Gutweed, one of their main food sources, grows in abundance on the peat and even when the birds are absent their droppings give away their presence in the area.

Away from the shore and the intertidal zone lives a group of animals that are locally known as the Shannon Dolphins. These bottlenose dolphins form one of only a few resident groups in the whole of Europe and have called the Shannon Estuary their home for hundreds if not thousands of years. One of the earliest accounts of the Shannon Dolphins could be the legend of the Cataigh (or Catach). This sea monster that claimed Scattery Island, a small piece of land in the middle of the estuary, was described as an enormous eel with a line of sharp barbs along the back, dagger-like teeth and long enough to curl around the island. As the monster devoured everything that came close, nobody dared to go even near Scattery. As in all good stories the monster met its match eventually, in this tale in the shape of the local saint named Senan. The saint defeated the Cataigh equipped with only a golden cross and the monster subsequently retired to Doolough Lake, a short trip north of the Shannon Estuary, where it has been leading a quiet life ever since. Because there is some truth in every legend it is likely that there really was a sea monster or in this case probably many of them. Witnessing a group of dolphins travelling, their fins cutting through the water, one could indeed imagine an eel like creature swimming along and up close the teeth of a dolphin appear very much dagger-like.

Today over 100 animals are present at the estuary at any given time. Of those around 40 are permanent residents, the others are coming and going throughout the year. The reason the estuary is so popular among dolphins is the same why birds like to come here: The rich food supply that is being brought in by the strong tidal currents. Bottlenose dolphins in general live on a diet of fish, squid and sometimes small crustaceans. The Shannon Dolphins are most likely mainly fish eaters and feed on resident fish like bass and various species of flatfish as well as pelagic species like herring or sprat that venture into the estuary. In late summer and autumn salmon becomes a major part of their diet and the animals can be seen tossing salmon in the air, a behaviour that is either associated with playing or learning or probably both. Dolphins are known for their very clever hunting techniques and in the Shannon they can be observed circling a school of fish to keep them together while individuals repeatedly dash into the tightly packed group to feed.

Bottlenose dolphins travel and hunt in small groups and find their way as well as their prey through echo location. While a dolphin’s eyesight is similar to our own it is only of very little use in the often murky waters of the estuary so echo location is a much more reliable method to get around. The dolphins emit a series of pulses and clicks from an area near their blowhole known as melon. When these sounds hit a solid object like a fish or a boat, they bounce back and the dolphin picks up those echoes through its lower jaw from where they are transmitted to the animal’s inner ear. Because sound travels five time faster in water than in air this way of experiencing the world is very effective. It is also though that certain variations of those clicks and pulses along with whistles are a form of communication between the animals. Tailslapping can also be a kind of communication. Depending on the strength of the slap this behaviour could be a warning to other animals or an attempt to make contact. Tailslapping has also been observed as part of hunting techniques. Other behaviours that can be observed are Spyhopping – the animal pokes its head out of the water to see what is going on above the surface –, Breaching – the animal jumps fully out of the water which could be another way to have a look around or just to have fun and Bowriding – possibly a way to save energy when swimming or yet another way to have fun. Dolphin groups can consist of up to 20 individuals but are on average considerably smaller. While these groups are very fluid, known as fission-fusion society, it is generally individuals of the same sex and age that travel together. Groups of mothers with calves for example can regular be seen in the Shannon Estuary.

Dolphins are not the only marine mammals in the Shannon Estuary. Other cetaceans especially minke whales regularly find their way into the area and bigger whales like humpbacks and orcas can be seen passing the headland of Loop Head. Common seals are regular visitors while grey seals are known to rear their young in the small storm beaches at the Mouth of the Shannon and the lower estuary. Unlike common seal pups, which are able to swim within hours after birth, the offspring of the grey seal is born with a white fluffy coat that needs to be shed before the youngsters can enter the water. This takes up to six weeks and during this time both mother and pup are stationary, the pup hauled up on the beach while the mother can often be seen patrolling the waters around the cove. Seals are the source of another legendary figure, the selkie, which is more commonly known as mermaid and which appears not only in local tales but is a common figure in legends all over Ireland as well as Scotland. Usually the selkie is trying to seduce and then cause harm to a fisherman that had done her wrong. Other stories tell of fishermen trying to trick the selkie into a life on land and spend their days in human form as the mother of the fisherman’s children. Otters are also common, but their secretive lifestyle makes them a most elusive animal. Otters feed mainly on fish and the size of their territories can range from 2 kilometres to 20 kilometres. The territories of coastal otters are usually smaller due to a better and more varied food supply while river otters often occupy very long stretches of their chosen waterway. Spread throughout their territory otters have a number of holts, underground dens, they use to rest and rear their young. These holts have usually more than one entrance with one almost always under water. Despite being seen very rarely the Irish otter population is one of the most stable in Europe and the Shannon Estuary is one of their strongholds.

Human life and wildlife have so far been coexisting in a delicate balance at the Shannon Estuary. While the estuary itself is a busy shipping lane and the shoreline has been fortified and built up for industrial use in many places there is sufficient room left for fauna and flora to thrive. This however doesn’t mean that all is perfect. The constant and ever-increasing shipping traffic causes significant noise pollution which can especially affect the bottlenose dolphin population. Industrial waste, sewage and run-off from pastures that can contain chemical elements from pesticides and fertilisers all find their way into the Shannon Estuary either directly or via its tributaries. Studies have shown that levels of PCB (Polychlorinated biphenyl) and other pollutants are present in the skin of the Shannon Dolphins and while the concentrations are not thought to be high enough to negatively affect the animals it gives reason to be concerned about the impact it will have on other wildlife. A growing concern is also the sheer amount of plastic that is being brought into the estuary through the tidal currents. The upper reach of the tide that was once marked by colourful seaweed accumulations is today a mix of seaweed, plastic bottles and other containers, fishing nets, cans and other flotsam and jetsam of human origin. One of the biggest environmental threats in the area and a long running controversial topic is the Aughinsh Alumina refinery. Red mud, also known as red sludge or bauxite tailings, is a waste product of the refining process that turns bauxite ore into aluminium. This red mud is highly toxic because of its alkalinity and at Aughinish it is being stored in large reservoirs close to the estuary. Any leakage could have a devastating effect on all wildlife in the Shannon Estuary and rumours about leakages, cover ups and health problems of local residents have been around for many years. The other two major industrial buildings, the power stations at Killimer and Tarbert, had their own share of problems over the years but are now in the process of being shut down as part of the climate action plan.

The future of the Shannon Estuary and its wild inhabitants hangs in an uncertain balance like it did for decades. In addition to existing threats the estuary will have to face increasing human pressure through a growing population and expanding tourism, rising sea levels and other impacts of climate change.

Carsten Krieger, Spring 2020 / Edited December 2020