Toxic algal bloom linked to marine animal stranding along Southern California coast
A toxic algal bloom impacting marine animals has been observed along the Southern California coast in late April 2025, according to experts. The event, producing the neurotoxin domoic acid, has resulted in the most severe dolphin stranding associated with a toxic algal bloom ever recorded in the region.
Satellite image showing the coastline of Southern California from San Diego to Ocean Side, captured on April 24, 2025. Credit: Copernicus EU/Sentinel-2, The Watchers
More than 50 dead and dying dolphins have been found along beaches in Los Angeles County over the past week, local authorities report. Other marine animals, including sea lions, minke whales, and gray whales, have also been affected.
The toxic algal bloom, stretching from San Diego County to San Luis Obispo County, is described by experts as the most severe dolphin stranding linked to a toxic bloom ever recorded along the Southern California coast. Additionally, this marks the fourth consecutive year with an algae bloom affecting Southern California’s marine life.
NOAA Fisheries’ Southwest Fisheries Science Center reported recovering 16 dead dolphins from San Diego beaches on April 20. Most were adult male long-beaked common dolphins, with a few short-beaked common dolphins and two pregnant females. Since March, the San Diego team alone has collected more than 50 dolphins affected by the bloom. Of the 14 dolphins tested so far, 11 showed high levels of domoic acid, and one tested positive for both domoic acid and saxitoxin, another marine neurotoxin.
Domoic acid, a neurotoxin produced by certain species of marine algae such as Pseudo-nitzschia, accumulates in fish and shellfish and moves up the food chain to marine mammals and seabirds. Affected animals often exhibit symptoms such as disorientation, seizures, and death.
Scientists attribute the bloom’s development to a combination of natural ocean upwelling, elevated sea surface temperatures, and nutrient runoff. Additional contributing factors may include increased nutrient loads from recent wildfire debris and urban runoff entering coastal ecosystems.
NOAA Fisheries stated that, despite the severity of the stranding, the current impacts are not expected to affect dolphin or sea lion populations on a broader scale. Population estimates include more than 80 000 long-beaked common dolphins, over 1 million short-beaked common dolphins, and approximately 250 000 California sea lions along the coast.
Authorities urge beachgoers to maintain a minimum distance of 46 m (50 yards) from affected animals and to report stranding via the Stranding Hotline at (866) 767-6114.
References:
1 Stranding Team Responds to More Than a Dozen Dead or Dying San Diego Dolphins in a Single Day – NOAA Fisheries – April 24, 2025
I'm a dedicated researcher, journalist, and editor at The Watchers. With over 20 years of experience in the media industry, I specialize in hard science news, focusing on extreme weather, seismic and volcanic activity, space weather, and astronomy, including near-Earth objects and planetary defense strategies. You can reach me at teo /at/ watchers.news.
Commenting rules and guidelines
We value the thoughts and opinions of our readers and welcome healthy discussions on our website. In order to maintain a respectful and positive community, we ask that all commenters follow these rules.