It remains unclear why hundreds of dead fish floated to the surface of Lake Apopka two weeks ago, state wildlife officials say.

Testing remains ongoing. No evidence points to an algal bloom or low dissolved oxygen levels in the water as the likely cause, according to the Florida Fish and Wildlife Conservation Commission, which reports it also received 31 reports of fish kills on the lakle between Jan. 31 and Feb. 11.

Cold temperatures can also trigger fish kills, especially if water temperatures drop suddenly or last for an extended period of time, the agency says. Other common causes include disease, herbicide, and spills of sewage or petroleum.

Orange County resident Andy Braddock calls Lake Apopka, Florida’s fourth-largest lake, his “happy place.” Braddock says he spends lots of time fishing on the lake and captured video of the fish kill after recently discovering the event while boating.