MERCED COUNTY (CBS SF) – State water officials have warned visitors to San Luis Reservoir in Merced County not to swim or fish due to the presence of toxic blue-green algae.

“This week’s lab results show an increase in toxin levels. A danger advisory was put in place today, and remains in effect for the entire lake until further notice,” the California Department of Water Resources said Tuesday.

Under the advisory, people and pets should stay out of the water and avoid contact with algal scum. The algal bloom can also accumulate into mats or form foam at the surface and along the shoreline.

Officials said the algae could range in color from blue, green, white or brown.

While boating is allowed, swimming and other recreational activities such as jet or water skiing is not recommended at this time.

Exposure to blue-green algae can cause eye irritation, allergic skin rash, mouth ulcers, vomiting and diarrhea, along with cold- and flu-like symptoms, officials warned. Pets are especially susceptible because they tend to drink while in the water and lick their fur afterwards.

Fish, along with mussels and bivalves, should not be collected from the area until the notice is lifted. Officials said visitors should also not drink, cook or wash dishes with untreated reservoir water, noting that camping filters, purification tablets or boiling do not remove the toxins.

Anyone who may have been poisoned by the algal bloom should seek medical attention immediately.