More than 300 fish suffocated in a river because of the hot weather.
Sussex Downs Conservation Board rangers removed dead flounder and plaice from the lower Cuckmere, near Seaford.
Temperatures reached about 23C (73F) in the shallow water, causing oxygen levels to drop.
Ranger Simon McHugh said the problem was being made worse because the meanders had become isolated from the main river and were silting up.
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