Some 25 tons of fish in a reservoir in the park will die when heavy sewage pollution, combined with high temperatures, deprives them of oxygen, the authority predicts.
The reservoir in Worsborough country park is one of the best coarse-fishing venues in the north of England, and the surrounding park with its old mill and demonstration farm is a favourite with schoolchildren. The authority is preparing emergency measures to save some of the fish by aerating the reservoir with portable pumps.
Sewage runs into the reservoir - built 200 years ago to top up Barnsley canal - and for years it was diluted by water pumped from coal mines. But now that the mines have shut the reservoir is being swamped with sewage. Yorkshire Water, the National Rivers Authority, and British Coal are all blaming each other for the problem.
Trevor Mayne, an area executive of the NRA, said: 'Yorkshire Water are gambling on . . . a cool summer and if they get away with it they will have saved a lot of money. But if we have a summer like '91, '92 or '93 the reservoir will go right off, and there will be the most terrible smell. A few fish may survive around the aerators, but it will take 20 years for the fishing to recover.'
British Coal offered to sell its pumps at Strafford Shaft, near Barnsley, to Yorkshire Water or the NRA so the dilution of sewage could be maintained, but neither considered that the pumps were their responsibility. 'We are very disappointed Yorkshire Water did not buy the pumps . . .' Mr Mayne said. 'They are responsible for proper disposal of sewage and this problem has occurred because Yorkshire Water reneged on a promise to build a new sewage works by 1993. We are very displeased with Yorkshire Water's approach so we have ordered them to reduce the ammonia in the effluent entering the reservoir and if they do not, we will be taking legal action.'
If the ammonia content is not reduced, blue-green algae will flourish, reducing oxygen in the water, particularly at night, starving the fish of oxygen and eventually killing them. Finally, the algae will die and the reservoir will be completely overgrown with bacteria.
Richard Hibberd, water quality manager with Yorkshire Water, said: 'We have an pounds 8m scheme which will solve the problem but it cannot be completed before summer 1997. In the meantime we are doing all we can to avoid a disaster. We are planning to set up temporary pumps to take the reservoir through the critical summer period.'