Lisa Attenborrow, who saw the
"I felt close to tears seeing hundreds of dying desperate creatures.
More than 500 fish were saved, but hundreds of roach and carp died. Birmingham city council said the fish were freed “inadvertently”.
Birmingham City Council admitted the fish, including roach, dace and carp, were released from a lake by its workers during checks on valves used in flood defences.
The authority, which issued an apology, said it would change its procedures to ensure there was no repeat of the accident.
A Birmingham City Council spokesperson said: "Our park rangers attended the site to retrieve as many released fish as possible.
"We are grateful to the local community and to the RSPCA for their assistance in this matter."