From floods to just centimetres of water. Scientists have warned of fish kills in the difficult conditions caused by low water levels. Extreme heat and low water levels cause reduced oxygen in lakes and rivers — this makes it difficult for fish to breathe and survive. Picture: Larry Cummins

Water levels were so low in the summer and early autumn that people wondered how fish could survive. Rivers that could be metres deep when in flood could be measured in centimetres.

From personal observation, stones in the nearby river bed were exposed for an unusually long period and rarely-seen rocks in the lake bed were also revealed, well out from the shoreline. Scientists warned of fish kills in the conditions.

We remember many such kills in the past, caused by the discharge of farm slurry, improperly treated sewage and industrial effluent into waterways. Thousands of salmon and trout were wiped out at the same time.

I have vivid memories of seeing so many fine fish killed in this way in some of Munster’s finest rivers: their white bellies turned up to the sun.  And I remember the protests of furious anglers.

Unfortunately, we still have kills of this kind. We would like to think that attitudes have changed compared to the situation in times past when there was widespread disregard for the environment. Waterways of every kind were treated like open sewers into which was poured all kinds of waste.

Cases of wanton disregard for water, and risks to people and animals which may be drinking it, still come before the courts. But, with climate change, lower than average rainfall and temperatures hitting over 30° Celsius, a different type of threat has emerged.

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All of which brings a high risk of fish kills for different reasons: ‘thermal stress’, caused by extreme heat and low water levels, and reduced oxygen in lakes and rivers, which makes it difficult for fish to breathe and survive.

According to Inland Fisheries Ireland (IFI), fish such as salmon and trout suffer thermal stress when temperatures exceed 20° Celsius.

Changing climate will mean more weather extremes; longer, warmer dry spells and, conversely, heavier rainfall over lengthy periods. But, traditional threats to water quality remain. 

For instance, 34 towns and villages released raw sewage into the environment every day in 2020, an EPA report disclosed. A third of these areas will not have a functional water treatment plant until after 2024.

The EPA has called for ‘substantial and sustained investment’ to bring public wastewater treatment up to standard, saying the pace at which essential improvements by Irish Water are being delivered is too slow. "There are repeated delays in providing proper treatment at many areas, and this continues to put our environment and people’s health at risk," Dr Tom Ryan, the EPA’s director of environmental enforcement, said.

Over the years, there hasn’t been enough investment and pressures are being increased by a growing population.

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