Last month's hot weather led to almost 50,000 fish deaths, according to the Environment Agency, whose teams across the country have been rescuing thousands of fish in distress.
Hot weather combined with low rainfall can make fatal conditions for fish, while heavy intense rain also leads to an increase in diffuse pollution as result of pollutants washed off roads, sewerage systems and from agricultural land.
Oxygen levels in the water can become dangerously low meaning that fish are at risk of suffocating or becoming more prone to stress and disease.
Due to the weather, July saw more than 15 separate incidents leading to nearly 50,000 fish deaths, however many more thousands were saved thanks to the swift action taken by EA teams and partners.
As experts predict that more hot weather is still to come, the EA is asking anyone finding distressed, diseased or dead fish in rivers to contact its incident hotline on 0800 80 70 60.
The tell-tale signs of fish in distress are gasping at the water’s surface or swimming on their sides or upside down.
If you're concerned about the effects of hot weather on your pondfish, check out our feature: How to ensure there's enough oxygen in your pond.
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