About 90 kilograms of dead fish were recovered from a canal in Walsall following a sodium cyanide leak that experts fear may have destroyed the “aquatic ecosystem” in the area.

A 1 km long section of the waterway remains closed to the public following the chemical accident at the metal finishing company Anochrome. The accident was declared a major incident last week.

Walsall City Council said tests had shown that a 300-metre section of the canal had been affected by the oil spill and that 90 kilograms of fish carcasses had been removed from the canal over the weekend.

“Numerous fish have been killed, but the impact on the overall ecology is not yet known,” the council said.

“Chemical testing continues daily and we are monitoring water levels. While we hope cyanide levels will decrease, we are evaluating all possible remediation techniques that may be required in the future.”

Temporary dams have been built on both sides of the affected red zone, where high concentrations of sodium cyanide and zinc cyanide were measured.

The Canal & River Trust is trying to raise £10,000 for the clean-up, calling the spill “extremely disturbing” and saying it is likely to cause great harm to local wildlife.

The charity’s chief ecologist, Paul Wilkinson, said: “The oil spill was contained to a relatively small area, but the impact on wildlife remains to be seen.”

“Unfortunately, we expect that the aquatic ecosystem in the section through which the pollution has passed will have been destroyed or lost, from the smallest invertebrates to the otter, which has its territory in this section. Without a natural balance, invasive species and algae will quickly take over: it could take years for the effects to fully recover.”

The aid organization said that “over 100 juvenile fish and dozens of large fish” had been killed and the number was expected to rise.

The council said water quality along the canal sections closed following the spill was in line with public health guidelines and normal activities could resume. It advised the public not to take or eat fish from the waterways.

The Environmental Protection Agency said it was investigating Anochrome following the oil spill and described the level of pollution as “unacceptable”.

Symptoms of sodium cyanide poisoning may include nausea, weakness, pain and loss of consciousness. The public has been asked to avoid direct physical contact with canal water along the affected section.