A toxic algal bloom known as Karenia mikimotoi was carried into South Australia’s Coorong, a 120-kilometer Ramsar-listed wetland near the Murray River’s mouth, by a storm event in late May 2025. The North Lagoon’s nutrient-rich waters were stained dark orange-brown by the algae’s fast reproduction, eventually turning the water into a slurry full of dead marine life. The algal bloom crisis in the Coorong Wetland has caused severe ecological damage and prompted urgent concern.

Estuarine biologist Faith Coleman said more than two hundred species were impacted. The deceased included benthic species, including coastal crabs, young flounder, estuary snails, and a thick stew of dead polychaete worms. For fish and shorebirds alike, these species are essential food sources.

Spores were still buried in the silt, even though levels had decreased since the peak. Coleman cautioned that the bloom would probably reappear as temperatures rose.

Climate and Nutrient Stressors Behind Recurrent Blooms

A report dated June 11, 2025, revealed elevated levels of chlorophyll, a sign of algae, throughout the western Gulf of Saint Vincent and the Coorong coast. The maritime warmth off South Australia still makes the bloom worse.

Gary Hera-Singh, a longtime fisherman, was one of the first to notice the brownish water. He said the bloom had destroyed “massive patches—100 acres at a time.” In his 41 years of fishing, he described this as the worst environmental incident he had ever witnessed.

According to Professor Peter Gell, a specialist in Ramsar wetlands, the Coorong has been deteriorating since the 1950s due to high nutrient loads, extended low river flows, and barrage equipment. He underlined that the bloom was a sign of more significant changes in the ecology, upsetting the food chain in the wetland and offshore.

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Urgent Restoration Efforts and Climate Resilience Needed

State and federal organizations are monitoring the situation and assessing the ecological effects over the long run. The Ramsar Convention requires Australia to report environmental damage in the Coorong.

According to the federal environment department, the dynamics of the North Lagoon may cause the algal bloom to continue. Coleman said that since the algae prefer salinity levels between 18 and 37 grams per liter, adding fresh water might help lessen the bloom.

The algal bloom crisis in Coorong Wetland has brought renewed urgency to local restoration. The Coorong Lower Lakes Murray Mouth Research Centre‘s Dr. Nick Whiterod called the occasion an “eye opener.” He cautioned that many ecosystems would soon lose their capacity to recover and connected the bloom to climate change.

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