Pike anglers are warning that Broads Authority plans to dredge Heigham Sound on the Upper Thurne could cause an ecological “catastrophe” by triggering a bloom of killer algae.

Pike anglers are warning that Broads Authority plans to dredge Heigham Sound on the Upper Thurne could cause an ecological “catastrophe” by triggering a bloom of killer algae.

And ahead of today's meeting of the Authority's planning committee which is being recommended to approve the scheme, Stephen Roberts, chairman of Norwich and District Pike Club (NDPC), claimed it could lead to direct action, with anglers already threatening to chain themselves to dredgers and hinder the operation with their boats.

The Authority is seeking planning approval to dredge Heigham Sound to increase the depth and width of the navigation channel and then use the spoil to restore an eroded strip of land that once separated the waterway from Duck Broad.

The plan has the backing of Norfolk and Suffolk Boating Association following instances of yachts running aground, most notably during the Three Rivers Race, and conservationists believe recreating the land strip would provide a more favourable sheltered environment for overwintering birds.

However, in a letter to today's meeting, the NDPC describes the plan as a “risk too far” and warns that the Authority will be held accountable if their worst fears are realised.

Its letters states that the Thurne system has never fully recovered from the decimation of an outbreak of fish-killing prymnesium parva in 1969, which had started in the Waxham area of Horsey Mere where dredging and pumping were being carried out.

It warns that prymnesium, which releases a lethal toxin when it dies, is an “ever-present time-bomb waiting to be triggered by the right conditions, aligned with any man-made activity that disturbs the nutrient-rich sediment”.

The anglers write that their fears are supported by experts in the USA and Israel, who warn against tampering with the natural environment where prymnesium is concerned.

They highlight the fact that the Thurne system is “the most renowned and important natural pike fishery in Britain with the largest ever English river pike on record from the River Thurne at 45lb 8oz”.

Dr Dan Hoare, the Broads Authority's waterways conservation manager, said prymnesium was a natural part of the brackish water ecology of the Upper Thurne and, as it lived in the water, not the mud, it would not necessarily be disturbed by dredging.

He said the dredging would be carried out cautiously with daily water quality checks, and added that the Authority and Environment Agency were working together to develop an emergency action plan in the event of a prymnesium outbreak, which included looking at ways to provide fresh water fish refuges.

Mark Casto, chairman of the Broads Angling Strategy Group, said anglers needed to keep their worries in perspective because without dredging, the Broads would silt up and all water life would die.