An Environment Agency (EA) team was last night trying to avert an ecological disaster with 100,000 fish in distress at a Broads beauty spot.

Fisheries officers were using aerators to pump oxygen into the water at Catfield Dyke, near Hickling, and netting the worst affected fish to take them in tanks on trailers to other parts of the River Thurne system.

The emergency is being blamed on the spread of the algae prymnesium parvum from neighbouring Hickling Broad where EA staff had to move 25,000 fish earlier this month.

The latest outbreak has sparked fears that the algae - deadly to fish but harmless to humans - could spread over a wider area and seriously affect the Broads' multi-million pound tourism industry.

The upper Thurne is regarded as one of the prime pike fishing spots in the country and local anglers fear fishing holidaymakers who have not yet booked will keep away after hearing of the prymnesium outbreak.

Hundreds of fish, mainly perch, are estimated to have perished on Hickling Broad but so far swift action by EA staff has restricted the death toll in Catfield Dyke to a few dozen.

Fisheries officer Tom Howard, leading the operation, said: 'We are monitoring the oxygen level with meters and in critical places netting the fish and moving them.

'We will be monitoring the situation throughout the weekend and will move all the fish if it becomes necessary.'

He said he was cautiously optimistic there would not be a serious spread of the algae as water tests away from the outbreak sites had shown much lower levels.

His officers have been using 35-metre nets to catch the fish in distress, which have included a number of pike in the range of 10lb as well as perch, bream and roach.

Mr Howard said that without swift action, there would have been a danger of many of the fish in the dyke perishing.

John Currie, a regional organiser for the Pike Anglers' Club of Great Britain, was at Catfield Dyke to help EA staff and said the fish in distress were clearly visible, coming to the surface where oxygen levels were low.

He said: 'They appear mainly to be roach but we are seeing bream and pike as well.'

Mr Currie confirmed that the algae - the most serious known outbreak of which devastated fish stocks throughout the Thurne in 1969 - had turned the dyke water a coffee colour.

As the disturbance of sediment, along with other factors such as warm weather, is a known trigger of algal blooms, Mr Currie repeated his appeal to the Broads Authority to stop work on its project to recreate a lost island in Heigham Sound at the edge of Hickling Broad.

He said: 'They were still working there on Thursday and I think that is irresponsible.'

However, a Broads Authority spokesman said their preparatory work for the dredging scheme had disturbed sediment no more than a passing boat would do.

Prymnesium levels had been monitored and had remained at less than half the danger level perceived by the EA.

She said the work at Heigham Sound - which was two miles away from the fish death sites - would be finished next week.

She added that their latest tests on whether prymnesium had even caused the fish deaths was still inconclusive.