Dudley Council said they have since been removed and council chiefs promised to keep an eye on the pool.
James O'Sullivan, 47, from Dudley, who took images of the fish at Mary Stevens Park, said: "It's a park that I walk around daily, I walk around at half six in the morning normally. It was a bit of shock, it was yesterday that I saw the smaller fish and today that I saw the bigger ones.
"I know there is a film on the water, they say it is an algae bloom. It's a shame really that the council won't invest in something more capable of protecting wildlife. There were brownies in the park yesterday that saw the fish, it's traumatising really."
The latest mass deaths come as reports flooded in of thousands of fish carcasses in West Park, Wolverhampton, and the River Tame in Elford.
James Reardon, 34, from Dudley, said: "I came walking down here and it looked horrible, there were hundreds of the things floating in the water.
Councillor Damian Corfield, Dudley Council’s cabinet member for highways and environmental services, said of the news: “We have sadly lost some of the fish population in the pool at Mary Stevens Park.
“We believe the deaths are due to the storms we’ve had this week, which can significantly reduce oxygen levels in the water. The dead fish have now been removed and we will continue to monitor the situation.”
Residents have also called for councils to be proactive with wildlife conservation, saying that councils should prepare for future weather events.
Mr Reardon added: "I think it's something that the council needs to do more about. They know this happens now, they should plan more in the future to save the wildlife we have. It's unforeseen circumstances, but now we know this happens, councils should do more to protect our animals."
Jamie Boyd, 28, a marine biologist from Wales, said: "Dry weather and thunderstorms can really affect the comfort of fish and severely reduce oxygen levels in the water due to the way that algae work.
"The reduced oxygen levels can put a lot of stress on aquatic life, even to the point of death, and reduced oxygen levels means that some fish will die from asphyxiation."