Orange County officials believe six broken aerators and algae growth caused low oxygen in the lake.
A fisherman was found safe after he went missing somewhere between Dana Point and Catalina Island, the Coast Guard said.
Máximo Napa Castro, 61, set off on his fishing boat on December 7 from Marcona, a coastal town in the south of the country, but bad weather caused him to stray from his course and lose direction.
Huntington Beach lifeguards increased patrols in the area after reports that two juvenile sharks were briefly caught by fishermen in the area.
Five people are missing after a fishing boat capsized near Point Couverden, Alaska, according to the U.S. Coast Guard.