AN algal bloom near Coffin Bay that resulted in fish and shellfish deaths has prompted an investigation by Primary Industries and Regions SA.
Testing of the waters around Coffin Bay to Port Drummond confirmed the presence of algae Karenia mikimotoi, a naturally occurring algae known to cause fish kills around the world.
According to PIRSA, the algae does not pose issues to human health.
PIRSA fisheries and aquaculture executive director Professor Mehdi Doroudi said tests conducted on abalone and oyster samples to rule out the presence of known infectious marine diseases had come back negative.
He said these types of blooms happened when environmental conditions were favourable.
"In this instance, dodge tides, high local water temperatures and the upwelling of nutrients from deeper waters, culminated in late February to make this particular algae increase in numbers, creating a bloom."
He said it caused localised deaths of species including abalone, cockles, rock lobster and fish on the reefs around Frenchman's Bluff, and a small number of fish deaths on the shore near Farm Beach.
"Testing of water and marine species occurred as soon as the bloom was reported.
"However, we have not had to close any areas or beaches as a result of the bloom because infectious disease and biotoxins are not present.
"PIRSA has been working closely with the fishing and aquaculture industry bodies to monitor the bloom's density and movement."
Professor Doroudi said the algal bloom was not affecting oyster leases in Coffin Bay, but if the situation changed lease holders had the option to move their oysters to alternative lease areas.
"Growers are encouraged to speak with their South Australian Oyster Growers Association Bay Representative."
South Australian Oyster Growers Association president Jill Coates said such a bloom was unusual and there had not been one in the area for almost 20 years.
According to SA Health, the species of algae involved in the bloom does not pose a human health risk, and live, healthy fish caught in the area are safe to consume.
However, people should not eat any fish found dead along the shoreline or in the water because of the normal risk of spoilage.
If you find large scale fish deaths in the region, report it to the 24-hour Fishwatch line on 1800 065 522.