AN UNUSUALLY large number of dead fish was found on the shores of Curtis Island over the weekend, concerning residents who believe the fish kill was in the thousands.
While the deaths coincide with the annual natural algae spread, locals say the event doesn't usually affect so many fish, or such large specimens.
The Environment Department is monitoring the situation, and have warned people that touching the slimy-looking algae could cause skin irritations.
Curtis Island resident Cheryl Watson, who saw the fish kill on Saturday, said it was an annual event to see a few small dead fish around, but this was something else.
"We're not saying it's anything but the algae but it's an unusual circumstance to have such a variety and large fish," she said.
"The photos really don't show up the extent of it, they were in patches and tangled up in seaweed."
A spokesperson for the Environment Department said the cause of the fish remains unclear but it could be related to algae.
"Trichodesmium blooms occur naturally in tropical and sub-tropical water in late spring/summer typically disappearing within a few days," he said.
"There was a similar incident at Facing Island in 2011."
Fish deaths can be reported to EHP through the Pollution Hotline on 1300 130 372.