Thousands of fish have been rescued from a dyke near the boatyard in Potter Heigham.
The Environment Agency were called to the scene on Tuesday after reports of fish gasping for air at the surface of the water.
After conducting tests, officers found that the oxygen levels were around 15-18pc, while levels in the adjacent River Thurne were 60-70pc.
By Wednesday morning, the oxygen levels in the dyke had dropped further to 4-5pc.
Across two days, using nets and water containers, officers transferred around 2,000 fish to the river, including pike, roach and perch.
Tom Howard, environment officer, said: “Obviously this hot weather is great for your sun tan but in terms of water, especially with low flow water, the oxygen level drops away because it’s just being used by plants and animals and it is not being refreshed.
“Fortunately we were able to get them back into the river and there have been no further problems.”
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