Heat, drought and pollution creating ‘lethal’ conditions for Ireland’s river life Inland Fisheries Ireland (IFI) has warned that a deadly mix of extreme heat, prolonged drought and pollution is pushing Ireland’s river ecosystems to breaking point. The agency confirmed it is investigating six major fish kills in the past six weeks, with two additional pollution incidents under review. These events have resulted in thousands of fish deaths, with the worst incident affecting a 2km stretch of the Cavan River near Cavan town, where at least 7,500 trout, eel, roach, lamprey and minnow perished. Other notable cases include over 400 fish dying in a 4km stretch of the Rye River in Co Kildare, and more than 120 endangered salmon found dead in the Dunkellin River in Co Galway. Fish kills have become increasingly frequent during the summer months, particularly between May and September, when warm weather and low water levels create ideal conditions for mortality. Dr Fiona Kelly, head of research, policy and risk at IFI, explained that high temperatures and reduced water flow are compounding existing environmental stressors. “Cold water fish, such as brown trout and salmon, require access to cold, clean water to remain healthy,” she stated. “Summer 2026, marked by prolonged dry weather and heatwaves, is creating extremely challenging conditions.” She noted that when pollutants enter already strained waterways, the risk of mass fish die-offs increases dramatically. Water levels across much of the country have dropped significantly, with many rivers flowing at less than a quarter of their usual volume. Data from the Environmental Protection Agency revealed that in July, most monitored rivers had below-normal flows, while records from the Office of Public Works indicated that water temperatures in several rivers exceeded safe thresholds for aquatic life. For instance, a temperature gauge on the Cavan River recorded 20 degrees Celsius during the fish kill, with readings previously reaching 22 degrees. Similarly, the Moynalty River saw temperatures of 19.5 degrees, and the Tolka River measured 21 degrees. These elevated temperatures, combined with low water levels, are leading to dangerously low dissolved oxygen concentrations in rivers, which can prove fatal for fish. As water levels decline, the remaining water becomes warmer and retains heat longer, often peaking in the late afternoon and staying high throughout the night. This lack of thermal relief leaves fish vulnerable to suffocation. “Low flows and high temperatures increase the likelihood of low dissolved oxygen concentrations, especially in watercourses with poor water quality,” Kelly said. “Together, these factors can create lethal conditions for fish.” IFI has expressed deep concern over the scale of the fish kills and the potential for further incidents. While most of the recent cases are being investigated, the agency emphasized that the situation could worsen as the summer progresses. “We are following definite lines of inquiry in relation to most of the recent kills,” Kelly added. The ongoing drought and heatwave have also contributed to the crisis, with many rivers experiencing unprecedented strain. Meanwhile, the agricultural sector continues to grapple with severe drought conditions. Farmers in the southeast and east of the country report that grass growth has effectively ceased due to a lack of rainfall, forcing them to rely heavily on stored winter fodder. Dairy farmer William Cassidy of Laois estimates that his herd is currently consuming full winter rations, costing him approximately €500 per day. Similar challenges are being faced by tillage farmers, whose crop yields have been drastically reduced. Soil moisture deficits in parts of the southeast reach up to 94mm, with some regions receiving as little as four millimeters of rain since early July. The outlook for relief remains bleak, with Met Éireann forecasting minimal rainfall for the affected areas over the coming week. While there is a slight chance of light showers in the southeast and east over the weekend, these are unlikely to provide meaningful respite. Farmers continue to express frustration over the lack of government support, with many calling for urgent intervention to mitigate the economic and environmental damage caused by the ongoing drought.
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