A man has called the scene of hundreds of dead fish in the river at the bottom of his garden as upsetting.
Peter Worboyes’s house backs onto the River Thet, in Thetford, where the dead fish can be seen across the river.
First reported to the Environment Agency over the weekend, the public body said the issue was caused by a fall in the river’s oxygen levels.
Levels fell to 11pc - at this time of year they are expected to be around 80pc.
“It is upsetting really to see all the dead dish,” said Mr Worboyes. “It is a natural occurrence and there is nobody to blame.
“I have been here 18 years and it has not been like this before. My neighbours have been here for 30 plus years and they say they have never seen this.”
The river is usually full of life with bream, roach and perch.
But with the fish laying on the river service in the heat, there is now a smell around the river and flies.
Mr Worboyes said he is frustrated with the situation and said he has been told by some agencies that due to the river being in private property, and do not present a health concern, the fish do not need to be collected.
An EA spokesman said: “Our fisheries officers are reacting to an average of two new incidents per day which is involving a lot of resource. As such we have had to prioritise larger mortality reports rather than minor incidents.
“In most cases we do not remove dead fish as this is a landowner’s responsibility-unless they pose a flood risk.
“Given the temperatures it is likely the fish in the Thet will have decomposed by the weekend and with the natural flow of the river, they then disappear into the river system.”
The Environment Agency said distressed and dead fish have been reported across East Anglia and more than 6,000 fish have been affected.
Rivers affected include the Stour, Deben, Gipping, Yare, Tud and Hickling Broad.
On Wednesday and Thursday EA officers were monitoring dissolved oxygen levels on the River Waveney between Scole and Billingford which were low.
They attempted to raise the levels to prevent an impact on the river and its wildlife.
Thousands of fish were rescued from a dyke near the boatyard in Potter Heigham.
The EA were called to the scene on Tuesday after reports of fish gasping for air at the surface of the water.
Across two days, using nets and water containers, officers transferred around 2,000 fish to the river, including pike, roach and perch.
An Environment Agency spokesperson said: “We have responded to an unprecedented number reports relating to fish in distress across East Anglia in the last few days.
“Our teams have been responding to reports by deploying aeration equipment and using hydrogen peroxide in affected stretches of river to boost oxygen levels.
“At this time of year we regularly respond to reports of fish in distress due to natural processes reducing oxygen levels in the water.
“In addition, when we experience a heavy storm after a long dry period, debris that has accumulated in the drainage systems is flushed into the rivers.
“As a result, the algae and micro-organisms in the rivers rapidly multiply which causes a significant drop in oxygen levels. This results in the fish being starved of oxygen.”
People are asked to call the EA if they see dead fish or fish gasping for breath. The hotline number is 0800 80 70 60.
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