Mass Qld fish deaths prompt water testing

Authorities have tested the water and begun aerating the water at a coastal lake north of Brisbane after thousands of fish died.

Thousands of fish deaths at a coastal lake north of Brisbane have prompted the authorities to do water tests as locals work to save the surviving fish.

Moreton Bay Regional Council says it's also begun aerating the water 24 hours per day to ensure a good supply of oxygen for the fish still alive in Beachmere Lake, near Caboolture.

"Council staff have collected water samples for laboratory analysis to investigate the cause of the fish kill," a spokesman told AAP on Monday.