Following the news that last month was the hottest June on record for the UK, the Environment Agency is asking the public to help look out for fish in distress during the prolonged warm weather.

Already this year, the Environment Agency has received more than 370 reports of fish in distress or dead fish—which is more than at this same point last year—and the Agency expects this figure to increase if predicted prolonged warm and thundery conditions continue.

High temperatures and low water flows, as we have seen recently, can result in low dissolved oxygen in rivers and waters in the UK. Lack of oxygen puts stress on the fish, and they can get trapped in shallow pools as water levels drop and escape routes dry up. In some waters, an increase in water temperature alone can kill large and sensitive fish species.

As water levels fall and temperatures rise in both still and flowing waters, algal blooms can also develop quickly and sap the dissolved oxygen from the water, putting large numbers of fish at risk.

Signs that fish are in distress include appearing lethargic or unresponsive, sometimes close to the bank; tight shoaling; and obvious gasping at the surface. Stressed fish can often show signs of infection or fungus.

Responding to fish in distress and fish kills is part of the Environment Agency’s service to protect fish stocks and the fisheries they support. Work includes deploying aeration equipment to help increase the amount of dissolved oxygen in watercourses, and where necessary relocating fish. Much of this work is funded by rod license income and the Agency delivers its service on all types of waters where freshwater fishing takes place. This includes rivers, still-waters, and canals both private and open to the public.

Members of the public who see fish in distress or see any blue green algae blooms should call the Environment Agency’s 24-hour freephone emergency hotline on 0800 80 70 60 so it can take action.

Dr. Graeme Storey, Fisheries Manager at the Environment Agency, said: “Environment Agency fisheries teams have been responding round the clock to numerous reports of dead or distressed fish across the country.

“While extreme weather including continuous hot temperatures and thunderstorms can be highly dangerous for fish, these incidents aren’t always due to a single cause and it is often the combination of several factors including temperature, water levels or flows, algal blooms, pollution, and fish disease that cause the effects we’re seeing.

“Emergency responses to such incidents can include reoxygenating water and rescuing fish where river flows are especially low.

“We encourage members of the public who see dead fish or fish in distress to contact our incident Hotline on 0800 80 70 60 and alert the fishery owner or angling club where possible.”

Climate change means we will see high temperatures more frequently. The Environment Agency recognizes the elevated risks to fish of prolonged dry and warm weather and continues to respond to incident reports, mitigating the impacts of recent high temperatures. As well as deploying aeration equipment and occasionally relocating fish, the Environment Agency also provides expert advice to angling clubs, fisheries, and anglers.

There are several ways in which warmer weather can lead to fish in distress:

• Blue green algae (cyanobacteria) becomes more common in warm conditions, particularly in lakes and ponds. It has the potential to be harmful by forming blooms and scums which can be highly toxic to humans, fish, and animals. Blooms noticeably discolor the water, making them easy to spot. They can vary from blue-green, green, or greenish brown, and should be avoided as they can be toxic and can lead to a variety of symptoms, including vomiting and diarrhea. For dogs and livestock, ingestion of scums can be fatal, so pet owners and farmers should keep animals away from the water. The Environment Agency provides advice and guidance to help reduce and control algal and cyanobacteria blooms, including the use of barley straw and aeration and where blue green algae bloom is confirmed works with landowners and other organizations to ensure necessary action is taken.
• Nutrient levels and other pollutants can build up on land because of the dry weather, meaning any downfall of rain will wash this pollution into waterways, upsetting the ecosystems there and putting fish in distress. The micro-organisms that cause algal blooms thrive off elevated pollution levels and this can therefore also leave to algal blooms. The Environment Agency provides advice to fishery operators on nutrient management, including management of fish stocks, bait types and other nutrient inputs, to help avoid these impacts.
• Thunderstorms can occur in warmer weather because there is more moisture in the air. Low atmospheric pressure during a thunderstorm can further reduce the capacity of the water to hold oxygen, which combined with other impacts of warm weather can be a final trigger for stressed fish to suffocate and die.

Advice for the public and landowners can be found at: https://www.gov.uk/government/publications/algal-blooms-advice-for-the-public-and-landowners/algal-blooms-advice-for-the-public-and-landowners