A massive bloom of toxic algae is killing more than 200 species of marine life off the southern coast of Australia, scientists and conservation groups say, according to AFP.

The algae, Karenia mikimotoi, appeared in the waters around South Australia in March, causing mass deaths of species including sharks, stingrays, crabs, and octopuses.

"The beaches are littered with carcasses," said Brad Martin, manager of the non-governmental fish conservation organization Ozfish.

"Often our volunteers say, 'We walked a kilometer along the beach and saw 100 dead stingrays and other marine animals,'" he said.

Beaches at tourist attractions rich in biodiversity such as Kangaroo Island, the Yorke Peninsula, and the Fleurieu Peninsula have been affected.

The bloom covers 4,400 square kilometers (1,700 square miles), Martin said — an area larger than Japan or Germany.

Karania mikimotoi has been found around the world since the 1930s, including off the coasts of Japan, Norway, the US, and China, where it has disrupted local tourism and fishing industries, causing millions of dollars in damage.

However, Martin pointed out that South Australia has not experienced a toxic algae bloom of this scale and duration before.

The South Australian government said the phenomenon is believed to have been caused by a marine heatwave, as well as relatively calm sea conditions.

Marine biologist Shauna Murray, who identified the algae species for authorities, said it damages fish gills and prevents them from breathing.

"It's not pleasant," Murray, from the University of Technology Sydney, said.

"It will probably take some time for the ecosystem to recover."

Although conditions usually improve by the end of April, there is still no relief, South Australia Environment Minister Susan Close said this month.

"It will take a significant change in the weather to overcome this phenomenon — there is nothing we can do to speed it up," she told national broadcaster ABC.

Meanwhile, authorities in South Australia have urged beachgoers to avoid swimming in water that is discolored or foamy, warning that it could irritate the skin and make breathing difficult.

Climate change has led to an increase in the frequency and duration of marine heatwaves in Australia, which is having a significant impact on marine ecosystems. |BGNES