SANTA NELLA - The Department of Water Resources (DWR) last Thursday issued an advisory urging 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 the presence of blue-green algae.

The DWR increased the advisory level from “warning” to “danger” after detecting an increased amount of microcystins. Boating is allowed, but swimming and other water-contact recreation and sporting activities are not considered safe under the danger advisory due to potential adverse health effects, according to a department news release.

The O’Neill Forebay remains free from algal bloom advisories, the DWR release stated.

Advisories are based on the potential health risks from algae. 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.

The advisory recommends keeping pets away from the water. Animals 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 may be blue, green, white or brown in color.

State guidelines on 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.