Press Release

'High Risk' of fish kills as water temperatures expected to rise

  • Warning from Inland Fisheries Ireland comes as fish population may be under ‘thermal stress’ because air and water temperatures are soaring, but water levels are dipping.
  • Water temperatures in excess of 20 degrees Celsius recorded this week on Lough Sheelin in Cavan and Lough Currane in Kerry. Elevated water temperatures increase risk of fish kills.
  • Appeal to public to report sightings of fish under thermal stress as anglers asked to voluntarily stop using ‘keep nets’ during heatwave conditions.

With Met Éireann forecasting a heat wave for large parts of the country, combined with lower-than-average rainfall, Inland Fisheries Ireland is warning that there is a high risk of fish kills due to thermal stress and reduced oxygen levels in lakes and rivers.

Also known as deoxygenation, reduced oxygen levels in a river or lake make it very difficult for fish to breathe and survive.

The state agency, which is responsible for the protection and conservation of freshwater fish and habitats, is concerned that water levels in many rivers are low and approaching drought conditions. Therefore, it is appealing to anglers, the farming community and the general public to report any sightings of fish under thermal stress, which may be caused by the extreme heat combined with low water levels and other pressures.

Anglers are also being asked to voluntarily stop using ‘keep nets’ while high temperature warnings from Met Éireann are in place, as these nets may cause unintentional distress to fish. In addition, anglers that practice ‘catch and release’ fishing are asked not to fish during the heat wave where possible, as this may put undue pressure on fish populations.

Dr Gregory Forde, Head of Operations at Inland Fisheries Ireland explains: “Unfortunately low water levels and high water temperatures can lead to fish kills, especially as there is less oxygen in the water to allow fish to breathe.  Once the water temperature exceeds 20 degrees Celsius, fish species such as salmon and trout suffer ‘thermal stress’. During the current heat wave, air and water temperatures are approaching dangerous levels and fish kills may be unavoidable. In some instances, moving fish in and out of the water may also prove too stressful.  That’s why we’re asking anglers practicing catch and release fishing to consider taking a break from fishing while high temperature warnings are in place. We’re also asking anglers to voluntarily stop using ‘keep nets’, until conditions become more favourable.”

In July, Inland Fisheries Ireland and the Office of Public Works’ data buoy* recorded a surface water temperature of 21.84 degrees Celsius at Lough Sheelin in County Cavan, coinciding with the hottest air temperature that month of 30.75 degrees Celsius. Inland Fisheries Ireland notes that significant thermal stress can occur in brown trout and other cold water fish species at temperatures at or above 20 degrees Celsius.

Forde said: “Inland Fisheries Ireland staff are continuously monitoring water bodies, such as rivers and lakes, for any signs of fish suffering thermal stress in shallow water or drying out rivers and streams. We’re encouraging the public to report any sightings of fish suffering thermal stress to our 24-hour confidential hotline on 0818 34 74 24 so we can respond as quickly as possible to help rescue or relocate these fish.”

“It is also a good time to remind all those using pesticides that these should be used only as a last resort, always in accordance with product instructions and always respecting statutory ‘no use’ zones, being mindful at all times of proximity to water bodies such as ditches, streams, ponds, rivers, lakes and springs. Even a very small amount of pesticide can be highly toxic to the aquatic environment,” he added.

To report sightings of fish suffering from thermal stress or fish kill incidents, members of the public are encouraged to call Inland Fisheries Ireland’s confidential 24-hour hotline number on 0818 34 74 24, which is open seven days a week.


For media information

Sarah Bohan

Communications Manager

Inland Fisheries Ireland


T: 087 65 39936


Notes to Editor

*Source of figures quoted: Lough Sheelin Lake and Climate Report July 2022, a joint initiative between Inland Fisheries Ireland and the Office of Public Works.

Figures from the Lough Sheelin water temperature and meteorology report for July 2022 show:

  • The maximum air temperature recorded in July 2022 was on July 18th. This temperature was 30.75 degrees Celsius.
  • The maximum water temperature recorded in July 2022 was on July 18th. This temperature was 21.84 degrees Celsius This water temperature was recorded at 0.5m below the water surface.
Low water levels at Owendoher River in Dublin 6

Low water levels at Owendoher River in Dublin

This image shows low water levels along the Owendoher River in Dublin 6, which is the largest tributary of the River Dodder. (Image taken by Inland Fisheries Ireland on 06.08.22)