South coast beaches are under increasing threat from warming waters, with thousands of dead cockles washing up on Goolwa Beach and polluted sea foam reported at Port Elliot and Chiton.

There have also been reports of a large fish kill at Island beach, on Kangaroo Island over the last week.

With an influx of visitors expected for the Easter school holidays, community and business groups have expressed concern about water safety, marine health and the future of local fisheries.

Parsons and Waitpinga beaches at Victor Harbor remain closed, as does the horse tram service to Granite Island, due to effects of the microalgae Karenia Mikimotoi.

This followed widespread reports of surfers and beachgoers suffering symptoms including coughing and breathing difficulties, itchy eyes and blurred vision.

The Environment Protection Authority (EPA) says most microalgal blooms in coastal waters occur naturally due to long hot periods combined with low winds and low tidal range.

January and February 2025 were the warmest on record for Australian waters in those months, according to the Bureau of Meteorology and CSIRO.

The March microalgal bloom outbreak has caused mass death of fish and other marine animals, including octopus, with yellow-green sea foam affecting beaches.

The EPA says the effects of marine heat waves go beyond harmful algal blooms, with seagrass and kelp particularly vulnerable.

RecFish SA has expressed concern about effects on commercial fisheries, covering areas from the south east to Tumby Bay.

It says the reported widespread death of pipis will likely impact breeding and commercial and recreational fishing of cockles.

SA Health has advised people to avoid swimming in affected areas and avoid discoloured water.

It says the toxic effect on fish does not have human impacts, but dead or dying fish should not be consumed due to spoilage.

For more information about marine heat waves and Karenia Mikimotoi, visit the EPA website.

Dead fish washed up on Kangaroo island. Image courtesy RecFish SA.