Sandwell Council figures show 30 Canada geese, four ducks and one coot died there between July 17 and August 16.
Severn Trent Water carried out repairs to sewage pipes contaminating the Smethwick Hall Park earlier this year and the company said it was not aware of any further problems.
But Ian Carroll, from Swan Watch, says there is still polluted silt at the site which is infecting birds.
He claims no action has been taken – over the polluted silt – because Sandwell Council and Severn Trent water are in dispute over clean-up costs.
Mr Carroll said: “If the contaminated silt is not removed, and the birds have access to this, they will continue to get ill.
“If they fly off and die elsewhere, as has happened, it could wipe out large numbers of birds, potentially at nature reserves.
“Sandwell Council are removing dead birds as they find them. Unfortunately not all of them will be found before the illness progresses.”
He added: “The council and Severn Trent is in dispute over who should clean up the silt.”
Mr Carroll says the birds died from botulism, a disease which is found in bacteria that exists in soil and water.
An RSPCA spokesman said: “We are continuing to help and assist in dealing with sick and injured birds such as Canada Geese and swans at Smethwick Hall Park.
“Last month alone we were called out on five occasions to carry out rescues of a number of birds at this location and sadly we have also had to retrieve the bodies of dead birds from the lake.
“Wherever we are able we are taking sick and injured birds for treatment and once rehabilitated they are released back into the wild at other locations.
“We have spoken to the local council and The Environment Agency about the situation at this lake and we hope they will be able to resolve the problem and the area will once again become a haven for local wildlife as it is a valuable natural asset to the local community.
“We will continue to monitor the situation but until this is resolved, we would ask anyone who notices any birds or other animals in distress to contact the RSPCA on 0300 1234 999.”
Severn Trent workers found several misconnections and placed a bung in a pipe to fix the problem in January, a report from the Environment Agency said.
The firm then visited the site in May after more reports of pollution.
A Seven Trent Water spokesman said: “We worked closely with the Environment Agency to improve the quality of the pool after a waste water problem earlier this year by pumping clean water in to help oxygenate certain areas.
“We also made changes to our network to ensure no further spills could occur, and are unaware of any issues on our system since May.”
A Sandwell Council spokesman said the issue is now a matter for Severn Trent.
Councillor Maria Crompton, cabinet member for safer communities, added: “Sandwell Council has been working with Severn Trent, the Environment Agency and a number of local residents and environmental groups to address this problem.
“We are actively seeking a resolution to this matter and will continue to do so. It is the responsibility of Severn Trent to address any contamination entering the pool and when this has been rectified we shall seek appropriate reimbursement for any remedial work required.”