San Luis Reservoir Algal Bloom at “Danger” Level

SACRAMENTO – Today, the Department of Water Resources (DWR) urged people to avoid physical contact with the water at San Luis Reservoir in Merced County until further notice and avoid eating fish from the lake due to presence of blue-green algae.

Boating is allowed, but swimming and other water-contact recreation and sporting activities are not considered safe under the danger advisory announced today due to potential adverse health effects. A warning level advisory had been in place at the reservoir since July 19. Today’s announcement elevates that advisory to a danger level. O’Neill Forebay remains free from algal bloom advisories.

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Danger signs are posted at the Basalt Boat Launch and Dinosaur Point Boat Launch.

The recommendation is based on the potential health risks from algal toxins. 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 can be especially susceptible because they tend to drink while in the water and lick their fur afterwards.

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

State guidelines on cyanobacteria and harmful algal blooms recommend the following precautions be taken in waters impacted by blue-green algae:

  • Do not let pets and livestock 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 algae 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 fish or shellfish from this water.
  • 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.

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