Fisherman Krisstian Smith made the grim discovery when he visited the park on Wednesday, weeks after he first raised the alarm of worrying algae in the water. He also said he had witnessed seagulls ‘falling from the sky’ after drinking the water.
Krisstian, who has fished at the lake regularly over the past four years, said it was normally ‘crystal clear’ and filled with fish.
But at the time, Birmingham City Council moved to reassure residents the lake was safe and ‘not hazardous’.
Steve Hollingworth, Birmingham City Council’s Service Director for open space and wellbeing, said: “Although the water is cloudy, it is a naturally occurring algae bloom and is not hazardous.
“We are satisfied that it is safe.”
Krisstian said: “I knew something was wrong at the start of June when there was a difference in the clarity of the water - which is usually crystal clear. My first thought was that it was blue green algae, which can be harmful to humans and animals. I reported it to the council who said it was safe. But this week, I was heartbroken to see thousands of dead fish and the few that remain are gasping for air.
The lake is usually full of bream, perch, tench, eels and carp. There is even a catfish in there. I would say around 90 per-cent of those are now dead. The pool is very popular with anglers but I doubt match fishermen will want to go there now On Tuesday, the council came down to remove the dead fish and aerate the lake but it’s too little too late.”
A spokeswoman for Birmingham City Council said: "The naturally occurring algal bloom, which is not hazardous but had made the water cloudy, has now dissipated. This caused a reaction which takes oxygen out of the water, putting the fish in distress. Following advice from the Environment Agency, two pumps have been brought into oxygenate the water and this process will continue until we are satisfied that the pool and fish are settled."