'Danger Advisory' issued for Castaic Lake: Here's why

California officials are warning the public to stay away from Castaic Lake due to a potentially dangerous algae bloom.

In a statement released Tuesday, the Department of Water Resources said this week's lab results showed an increase in toxin levels in the lake. 

The "Danger Advisory" issued Tuesday is in effect for all of Castaic Lake except Castaic Lagoon until further notice.

At this time, officials said boating is still allowed, however, water-contact recreation and sporting activities are not deemed safe due to "potential adverse health effects."


Exposure to toxic blue-green algae, also known as cyanobacteria, can cause eye irritation, allergic skin rash, mouth ulcers, vomiting, diarrhea, and cold- and flu-like symptoms.

Pets are especially vulnerable and it is advised to keep them away from the water.

File photo of Castaic Lake on April 22, 2023, in Castaic, California. (Photo by George Rose/Getty Images)

"Bloom conditions can change rapidly, and wind and waves may move or concentrate the bloom into different regions of the reservoir," state officials said. "The algal bloom can accumulate into mats, and scum, form foam at the surface and along the shoreline, and range in color from blue, green, white, or brown."

Officials have issued the following tips:

  • Take care that pets and livestock do not drink the water, swim through algal blooms, scum, or mats, or lick their fur after going in the water. Rinse pets in clean water to remove algae from fur.
  • Avoid wading, swimming, or jet or water skiing in water containing algal blooms, scum, or mats.
  • Do not drink, cook, or wash dishes with untreated surface water from these areas under any circumstances. Common water purification techniques such as camping filters, tablets, and boiling do not remove toxins.
  • Do not eat mussels or other bivalves collected from these areas. No fish should be consumed under a danger advisory.
  • Get medical treatment immediately if you think that you, a family member, friend, pet, or livestock might have been poisoned by blue-green algae toxins. Be sure to alert medical professionals to the possible contact with blue-green algae. Also, make sure to contact the local county public health department.

For more information, visit the California Dept. of Public Health's website.