There has been a steady stream of bad news about our rivers in recent weeks. Two fish kills occurred in quick succession, one in the River Rye in Co Kildare this month, and another last month in the River Glyde in Co. Louth. Agricultural pollution is believed to have caused the first, while the second remains under investigation. In response to the increasing frequency of such incidents, Inland Fisheries Ireland has introduced a national interagency protocol to coordinate investigations. Closer to home, the impact of the 2021 fish kill on the River Ilen is still being felt, in which an estimated 2,000 fish were lost due to industrial discharge. Local anglers continue to express concern about declining fish numbers, particularly salmon. While fish kills are an immediate and visible problem, they sit within a much broader and more worrying trend. Atlantic salmon have declined by around 90% in the past 50 years.

Salmon decline

The causes behind this decline are multifactorial, making recovery difficult, as there is no single solution. A valued inhabitant of local waterways such as the Glengarriff, Coomahola, Ilen, Bandon, and Argideen rivers, salmon feed in the Atlantic Ocean when mature, but return each spring and summer to the river where they were born to mate and spawn.

Water quality is critical to the salmon’s survival. They depend on unpolluted, well-oxygenated water, not only for reproduction, but also to maintain the invertebrate populations that they feed on in their juvenile stages. Pollution from agriculture, industry, wastewater, herbicides, and pesticides all place pressure on water quality. At the same time, habitat loss and river modification lead to increased silt entering waterways, which can smother spawning grounds. Barriers such as weirs and dams disrupt migration routes, while salmon farming can expose wild salmon to lice and disease. Even at sea, they face significant threats as bycatch in commercial fisheries. Climate change compounds all of these pressures, with rising water temperatures placing further strain on already vulnerable populations.

Freshwater pearl mussels

Alongside salmon, another species quietly signals the health of our rivers. The freshwater pearl mussel, once widespread in clean, fast-flowing rivers, has undergone a dramatic decline. They can live for more than a century and require exceptionally high water quality, making them a sensitive indicator of change. Their decline mirrors that of salmon. Excess silt can smother juvenile mussels living within the riverbed, while nutrient pollution reduces oxygen levels. Their life cycle also depends on salmon and trout, so falling fish populations place them at even greater risk. I often find the empty shells of the freshwater pearl mussel downstream on the banks of the Ilen. The sad reality is that many populations are now functionally extinct, adults still survive, but conditions are not suitable to allow enough successful reproduction to sustain the population long-term.

Water quality

Water is life. As the saying goes, you never miss the water until the well has run dry. Healthy freshwater systems support wildlife, provide drinking water, and shape our landscapes, as well as underpinning recreation and tourism. Understanding how healthy rivers work literally starts at the bottom, with aquatic invertebrates living in the riverbed. These creatures include stoneflies, mayflies, and caddisflies, and play a vital role in maintaining river health. These insects spend most of their lives underwater before emerging briefly as adults, some live for just a day-only long enough to reproduce. During their aquatic phase, they break down organic matter, recycle and manage nutrients, filter water, and help to stabilise the riverbed. Caddisfly larvae, in particular, construct protective cases from sand and gravel. Research suggests that a two kilometre stretch of river can contain 128 million of these cases, binding eight tonnes of sediment. In doing so, they quite literally hold the riverbed together. These invertebrates form the foundation of the food web. Fish depend on them, while otters and kingfishers rely on fish. Even swifts, swallows, and sand martins rely on rivers and lakes for nesting materials and for the insects that emerge from the water. As the famous ecologist Aldo Leopold once said, ‘To keep every cog and wheel is the first precaution of intelligent tinkering’. Aquatic invertebrates are essential to the functioning of river systems, and they also act as early warning signs when something is wrong.

Take action

While the decline of our rivers can feel overwhelming, there are ways to take positive action. This summer, Green Skibbereen is running a series of six hands-on outdoor workshops along the Ilen catchment. Participants will learn to identify aquatic insects, understand which species indicate good or poor water quality, and build a clearer picture of river health. It is an opportunity to learn practical skills such as monitoring water quality, identifying invasive species, and recording biodiversity. The data collected contribute to national monitoring schemes and help to inform how rivers are managed. If you would like to get involved, you can contact Ana at [email protected].

Otter on the banks of the Ilen. (Photos: Nick Haigh)