The current heatwave and a possible blockage in a pipe supplying fresh water to the pond may be to blame.

Robin Goldsmith (67), of Raby Avenue, North Lynn, said he regularly fished in the pond off Loke Road, catching various species including carp, roach and perch.

On Tuesday morning, he estimated there were 50 dead fish floating on the surface before council workmen took them away. Many others were "swimming round gasping for air."

Mr Goldsmith feared a pump which feeds fresh water into the pond was not turned on.

He also said there appeared to be a blockage under the road separating the north and south sections of the pond. Jetting engineers had been seen trying to clear the obstruction.

On Wednesday, the water level in the northern section had risen by about 15 centimetres but was still lower than it should be and there were still some dead fish, he said.

His wife, Rita (63), who usually fishes in the pond every day, said: "It breaks your heart to see the fish."

Another angler, Mr Gareth Rudd, of North Lynn, hit out: "Something needs to be done. The council needs to take a bit of time to keep the pond clean."

Mrs Beverley Howard, of St Edmundsbury Road, North Lynn, said: "Everyone goes down there fishing and it is going to be destroyed. I have never seen fish dying like that."

The Environment Agency was alerted late on Sunday and checks carried out early on Monday showed the water in the pond was low in dissolved oxygen.

A spokesman said: "The pond was dosed with hydrogen peroxide to boost oxygen levels, which have now risen. We are are continuing to monitor the situation."

West Norfolk Council's portfolio holder for the environment, Cllr Brian Long, said: "We are exploring every avenue to do what we can to save the fish."

Further attempts to jet through the apparent obstruction between the ponds were made on Wednesday afternoon, he said.

It was possible that a blockage had been caused by someone throwing litter or rubbish into the pond.

"The actions of those thoughtless people could well be leading to the demise of the fish," said Cllr Long.

The pump which tops up the ponds was not capable of running for 24 hours continuously but had been fitted with a timer so that the maximum possible amount of water was feeding through, he went on.

However, the hot weather was causing the water to evaporate far more quickly than usual.