As of April 21, harmful algal bloom (HAB) monitoring by SCCOOS has detected elevated levels of saxitoxin-producing dinoflagellate (Alexandrium) in the waters off Santa Monica. Meanwhile, the algae responsible for producing domoic acid (Pseudo-nitzschia) are still being detected off our coast and show significant spikes in March and April. This dual bloom event may intensify the impacts on marine wildlife, contributing to the recent surge in animal distress and mortality along our coast.
If you see a distressed or deceased marine mammal, it’s important to stay safe and protect the animal by working with local authorities, including lifeguards. Never approach, touch, or attempt to move an impacted animal. Read on to learn more about this algal bloom, how to report marine mammals in need, and how to stay safe.
Southern California is currently experiencing a significant harmful algal bloom (HAB) that poses serious threats to marine life and public health.
You may have recently seen disturbing reports of disoriented sea lions or deceased dolphins along the California coast. These marine mammals are experiencing the effects of harmful neurotoxins due to a toxic algal bloom. As the number of beached and injured animal cases rises, so does the spread of misinformation about their cause, their impact on marine life, and whether it’s connected to recent wildfires. Heal the Bay’s science team is here to break down the facts about this bloom and share what beachgoers, anglers, and coastal communities need to know to stay informed and safe.
The Bloom Below the Surface
Current Status of the Algal Bloom
The recent bloom was first detected in San Diego in December 2024, but the toxic algal bloom intensified in mid-February as it moved into Los Angeles County. It has now spread along the entire Southern California coastline and into Baja, affecting all Southern California counties from San Diego to Santa Barbara, and is now being detected along Central California waters as well.
What type of algae is this?
This bloom is primarily caused by the algae species Pseudo-nitzschia, a type of phytoplankton that produces domoic acid, a potent neurotoxin that causes domoic acid poisoning, also referred to as Amnesic Shellfish Poisoning. However, this is a unique and somewhat unprecedented bloom as we are also seeing another plankton, a type of dinoflagellate, blooming and producing saxitoxin, a different and yet equally dangerous neurotoxin that causes Paralytic Shellfish Poisoning. Marine life has been severely impacted, with reports indicating that hundreds of sea lions, dolphins, whales, and seabirds have been affected. These toxins accumulate in shellfish and small finfish such as sardines and anchovies, which are common prey for these marine animals, leading to neurological symptoms such as disorientation, seizures, and death.
Red-hued algal bloom appearing in SoCal waters. Photo by Laura Rink, Associate Director of Operations for the Heal the Bay Aquarium.
Are these types of algae blooms natural or unnatural?
While harmful algal blooms are natural occurrences in California’s marine ecosystems, their frequency and intensity are exacerbated by climate change and pollution. Warmer waters, increased nutrient runoff, and increased winds leading to increased upwelling (a natural occurrence that brings nutrient-rich water up to the surface from deeper water) create an ideal environment for algae to bloom. This is the fourth consecutive year that Southern California has experienced a severe, harmful algal bloom.
Did the January 2025 Wildfires cause this event?
We cannot definitively link this bloom to the wildfires, considering that high algal levels were detected before the fires began, and impacts from domoic acid have been observed for the last four years. However, it is possible that the post-fire conditions contributed to the algal bloom’s intensity this year.
The same high winds that intensified the firestorm also may have increased nutrient upwelling. After the fire, heavy rains washed nutrients such as sulfates, nitrates, and phosphorus found in ash and fire retardants onto the coastline. This influx of nutrients into coastal waters can stimulate the growth of algae, including harmful species. Additionally, wildfire ash can introduce iron into marine ecosystems, further promoting algal proliferation, but we do not yet have sufficient scientific evidence to see a definitive correlation between this year’s megafires and this year’s harmful algal bloom.
Wildlife Encounters & Seafood Warnings
What do I do if I encounter sick or injured marine life on the beach?
Photo: VALERIE MACON / AFP / Getty Images
While we have experienced serious, harmful algal blooms and domoic acid outbreaks for the past few years, this particular bloom affects even more animals than we have seen recently, including sea lions, seals, and dolphins. If you are visiting the beach, you may come across wildlife that is affected by domoic acid poisoning. The public is urged to exercise caution when encountering marine animals that appear sick, injured, or deceased. DO NOT APPROACH ANY ANIMALS.
Domoic acid poisoning can cause marine mammals to exhibit unusual or aggressive behavior, posing potential risks to human safety. As many Angelenos have probably heard, there have been recent incidents of sea lions exhibiting aggressive behavior towards humans, likely due to domoic acid exposure. These animals are also very sick and need space to avoid harming them further. While it is always illegal to approach a marine mammal due to the Marine Mammal Protection Act, it is critical to exercise caution now. If you come across such animals:
- Do Not Approach: Maintain a safe distance to avoid potential injury to you or the animal. Do NOT touch the animal.
- Contact Authorities: Report the sighting to local marine mammal rescue organizations or wildlife authorities.
- To report a live marine mammal in need, call the Marine Mammal Care Center’s hotline at 1-800-399-4253
- To report a deceased marine mammal from the Southern Border of LA County to the City of Malibu line, call the OARRA hotline at 949-276-2237
- To report a stranded marine mammal in Malibu, call NOAA’s Malibu hotline at 866-767-6114
- Follow Instructions: Provide accurate information about the animal’s location and condition, and follow any guidance provided by authorities.
Is it safe to swim in the algae-abundant waters?
When the “red tide” comes in, some surfers won’t hesitate to risk the pungent waters for the perfect break. But is it safe to be in the water during a visible algae bloom? While domoic acid and saxitoxin are generally only dangerous to humans when consumed in affected seafood like shellfish, they don’t pose a significant risk to swimmers. That said, the marine life impacted by this outbreak may behave erratically, which can pose a risk to recreators. Risk is a personal choice, however we at Heal the Bay don’t recommend swimming in affected waters out of an abundance of caution.
Can I eat locally caught shellfish?
Humans can get very sick from eating shellfish that have been contaminated with domoic acid and/or saxitoxin. In response to the elevated levels of these toxins in samples, the California Department of Public Health (CDPH) has issued multiple shellfish advisories in the past month.
The advisories warn against the consumption of recreationally harvested mussels, clams, oysters, and scallops from San Diego, Orange, Los Angeles, Ventura, and Santa Barbara counties due to the risk of Amnesic Shellfish Poisoning (ASP) and Paralytic Shellfish Poisoning (PSP). 
Symptoms of ASP can range from gastrointestinal distress to severe neurological issues, including memory loss. Symptoms of PSP begin with tingling around the mouth and fingertips, followed by loss of balance, lack of muscular coordination, slurred speech, and difficulty swallowing. In severe poisonings from either ASP or PSP, death can occur.
What does this mean for seafood lovers? Stay away from locally caught shellfish for now to stay safe until this bloom dissipates – cooking does NOT eliminate these toxins from food.
Should I stay away from commercial shellfish products?
Commercial shellfish products remain safe for consumption, as they are subject to rigorous testing before reaching the market.
Heal the Bay’s Initiatives and Resources
Heal the Bay remains deeply committed to safeguarding the health of our coastal waters and marine life and the public health of all Angelenos. In light of recent wildfires and their potential impact on ocean health, we have launched the “Ash to Action” initiative, focusing on monitoring and mitigating wildfire-related pollutants in our waterways. Our dedicated water quality scientists have worked around the clock to collect, test, and analyze water samples from in and around the burn zone and we recently published those results to keep the public informed. We will continue to work with local County and City officials and other scientists to gather and disseminate information about post-fire water quality. To stay up to date, follow us on social media @healthebay, subscribe to our newsletters, and bookmark the Ash to Action splash page.
For more information, watch our recent webinar with the Marine Mammal Care Center where we answer questions about this harmful algal bloom. Click here to watch. Password: WELOVE0URBAY! (the “O” in “OUR” is a Zero)
Note: This information is based on the latest available data as of April 24, 2025. For real-time updates and advisories, please refer to official sources such as the California Department of Public Health, SCCOOS HAB Bulletin, and local wildlife authorities.
