Council and health chiefs are probing the death of several birds at Lakeside over the past week - but have said the incident is not on the scale of a recent series of problems at Sandall Park where dozens of ducks have died and where the lake has been sealed off because of deadly blue green algae.
The bodies of several birds have been spotted floating in the water at the man-made lake visited by hundreds of walkers, runners and cyclists each day.
Doncaster Council has issued a statement and said that "no specific problem" for the deaths of the birds had been established.
A spokesman said: “We are aware of a small number of aquatic birds at Lakeside that have died recently and we are working with The Animal and Plant Health Agency to identify the cause of death.
"So far we have not established a specific problem like the one experienced at Sandall Park.
“We regularly check all lakes and ponds on council land and latest water samples show that no blue green algae has been detected at Lakeside.
"At Sandall Park blue green algae has been confirmed and we are working with the Environment Agency to address the algae which is likely to take a number of weeks to clear.”
There have been unconfirmed reports that some of the ducks at Lakeside may have been shot with a pellet gun by a group of people spotted on one of the island's lakes over the weekend.
Meanwhile, the lake at Sandall Park remains closed after blue green algae was confirmed. Visitors and animals are being urged to stay away from the water while experts work to resolve the issue.
Earlier in the summer, more than 100 ducks died after being poisoned by rotting vegetation within the lake.