The Environment Agency is urging caution after the hot and humid conditions caused an algal bloom on the River Great Ouse, in Ely.
A vast stretch of the river – from Ely to Queen Adelaide – has been turned green under a carpet of algae, raising concerns about the health of fish and other wildlife in the area.
Algal blooms are short lived but when they die and start to decay, they use a lot of oxygen from the water, effectively suffocating other animals and plants.
A spokesman for the agency said that anyone who spots the algae should report its location to officials via the customer contact centre.
The spokesman added: “In the meantime it would be wise for people and pets to stay away from it.”
To contact the Environment Agency, call 03708 506506.
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