The River Dargle springs to life amidst a marshy bog on the northern slope of Djouce Mountain, approximately 3.5km west of where you stand. After making a magnificent descent at Powerscourt Waterfall, the river flows north-east for a further 16km, passing through Enniskerry and the scenic Dargle Glen in a series of rapids and waterfalls before entering the Irish Sea at Bray.
These mountain waters create a fantastic habitat for the great variety of flora and fauna that call this river home.
Having spent the first two years of their life in the upper reaches of the River Dargle, salmon migrate hundreds of kilometres out to sea. Their destination is the rich feeding grounds off the coast of Norway and Greenland, where they will stay for up to four years. Using the currents and chemicals in the water, they then navigate back to the river and battle upstream to spawn, often in the very gravel where they themselves hatched.
Unlike their close relative the salmon, brown trout spend their whole lives in fresh water. Trout are very busy fish, always swimming against the current looking for a passing meal, or darting around fiercely defending their territory from intruders. To keep up this active lifestyle, they need a lot of oxygen. The clean water that splashes over the boulders and waterfalls of the River Dargle is full of oxygen taken in from the fresh mountain air, making it the perfect habitat for them.
Sea trout are in fact brown trout which have adapted for life in both fresh and salt water. Attracted by the increased availability of food the coastal waters offer, they spend most of their lives in the sea, only returning to the rivers in which they began life to breed and spawn. The Dargle is one of Ireland’s prime sea trout rivers, and the big fish that can be caught here make it very popular with local anglers.
Mayflies are best known for their brief adult existence as delicate flying insects with long, thread-like ‘tails’ which trail behind in flight. Nicknamed ‘dayflies’, they commonly die within hours of taking flight, surviving only long enough to reproduce. However, they spend the majority of their lives in an aquatic immature stage (nymph), clinging to stones along the riverbed and feeding on microscopic algae. Here they are a favourite food of fish, and many fishing flies are made to resemble them!
Another flying insect with an aquatic larval stage is the caddisfly. These incredible insects are closely related to butterflies and moths, and their larvae are able to spin silk like caterpillars. Many of these underwater architects make protective cases for themselves, binding the silk with tiny stones, sand and small pieces of twig, which keeps them from being swept away in fast-flowing water. After a year or two the larvae turn these cases into cocoons before emerging as adults. Caddisflies are very sensitive to pollution, and their presence in a river is used to indicate the quality of the water.
The damp banks of the river favour the growth of ferns such as the large bracken, which is common throughout Ireland. Ferns have been on the earth many millions of years longer than the flowering plants and do not have seeds. Instead they have fine, dust-like spores, which are shed from the underside of their leaf-like fronds.
Soft carpets of bright green moss cover the stones and boulders along the riverbank, and creep their way up trunks and branches on the shaded sides of trees. Mosses absorb water and nutrients through their leaves, rather than through roots, so they need to live in damp places to survive!
Tufts of the tall, shiny, dark green stems of rushes can be seen sticking out of the grass along the banks of the river. These spiky plants are traditionally used to make St. Brigid’s crosses, which are usually made on February 1st, and are said to protect a house from fire.
Otters live near the riverbank in dens called ‘holts’ and hunt during the night, swimming and diving in the river for salmon and trout. Due to their nocturnal behaviour and large territories (a single otter can have a territory of up to 20km) these animals can be quite elusive! However, you might be able to tell their presence from muddy slides along the edge of the river, as otters nearly always leave the water at the same place.
The stout, short-tailed dipper is one of the most common birds seen along the River Dargle. Look out for it flying at speed, low over the surface of the river, before it dives below the water in search of mayfly larvae.
The energetic grey wagtail, with its bright lemon-yellow chest, can often be seen perched on rocks in the river, wagging its long, slim tail up and down as it searches for flying insects.
Should you catch a glimpse of something swooping low over the water in the evening, it is most likely a Daubenton’s bat. This medium sized bat is like a small hovercraft as it skirts only a few centimetres above the surface of the water, catching midges, mayflies and caddisflies.