Dead fish were found in a west-end Toronto pond. Authorities are trying to find out why

Provincial and local authorities are investigating after several dead fish were discovered in Topham Pond in Toronto's Eglinton Flats park over the weekend.

Video on social media showed the pond's shoreline buzzing with flies and dotted with the remains of several small fish and a few larger fish. 

The Toronto and Region Conservation Authority (TRCA) and Ontario Ministry of Environment, Conservation and Parks said an investigation is underway to determine the exact cause for the fish die-off, but that it could likely be a natural occurrence. 

"TRCA is working with the city to address this situation and have shared that recent temperature fluctuations in the past few weeks may be a natural cause of the dead fish in the pond," said the ministry in a statement. 

The ministry added there was no evidence of any chemical spills in the vicinity that could have caused the fish to die.

Jacek Pawlikowski, a microbiologist who happened to be near Topham Pond on Tuesday, said other dead animals would have been found in the park had there been a chemical spill. 

Instead, he believes the fish died from algae blooms, a sudden overgrowth of algae in a short period of time, that eventually died and consumed the oxygen in the water. 

"Every year, we have some lack of oxygen and it's coming from the decaying algae… [which means] fish are dying," said Pawlikowski. 

"The blooming algae and then lack of oxygen at the last stage when they are decaying underwater is normal around the world."

According to a Facebook post in the Toronto Fishing Club group, a family fishing event on Saturday was cancelled following concerns from the "significant" fish die-off and the resulting investigation. 

TRCA said in a statement that it would work closely with the City of Toronto for any necessary cleanup or remediation.