South Australian harmful algal bloom: 2025-2026
Last updated: 14 February 2026.
Since the middle of March 2025, South Australian coasts have been afflicted by a toxic algal bloom of unprecedented size and duration. The effects of the bloom on marine life have been devastating, with untold thousands of dead creatures, from tiny worms to large sharks, washing up on the beaches from Encounter Bay and Kangaroo Island to shores on both sides of Gulf St Vincent. Underwater surveys indicate that mortalities seen on the beaches are only a small fraction of what is happening off-shore.
Initially, one of the dominant organisms originally identified in the bloom was a dinoflagellate, Karenia mikimotoi. It is highly cytotoxic, although the precise mechanism of its primary toxic action is still not fully understood. In November, 2025, another species, Karenia cristata, was identified as a dominant species in many samples of the bloom. It is a significant producer of brevetoxin, which has well-described neurotoxic and respiratory actions. Other species of dinoflagellates detected to varying degrees in the bloom include Karenia papilionacea which also produces brevetoxin, Karenia brevisulcata, which produces a brevetoxin-like toxin and a cytotoxin, and Karlodinium species which produce a range of karlotoxins, which are … Click here for more.
