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Toxic Algae Bloom Along Southern California Coast Reaches Unprecedented Scale

The ongoing harmful algal bloom, producing the neurotoxin domoic acid, has caused record marine animal deaths, including dolphins, sea lions, and now whales, overwhelming rescue efforts and raising urgent ecological concerns.

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Teams from PMMC and OARRA take samples of the whale so that NOAA teams can study them for domoic acid poisoning. (Photo courtesy of PMMC)
Dead whales stranded in April 2025 in Huntington Beach and Long Beach.
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Overview

  • The toxic bloom, spanning from San Luis Obispo to San Diego, has been designated an extreme danger zone by health and environmental groups due to its severity.
  • Necropsies confirmed domoic acid poisoning as the cause of death for a humpback and minke whale, with tests pending for two gray whales stranded in the region.
  • Over 200 marine animals, including record numbers of dolphins and sea lions, have been affected, with rescue centers struggling to keep up with daily strandings.
  • Of the 14 dolphins tested by NOAA, 11 showed high levels of domoic acid, and one also had saxitoxin, indicating multiple toxins in the marine food web.
  • Experts attribute the bloom's intensity to warming ocean conditions, fertilizer runoff, and wildfire debris, highlighting long-term ecological imbalances.