Avoid swimming here: Algal mats discovered in Sequoia National Forest, San Joaquin River

FRESNO COUNTY, Calif. (KSEE/KGPE) – Dangerous algal mats have been reported at a popular campground in Sequoia National Forest and a site on the San Joaquin River.

Algal mats are dense, sheet-like accumulations of algae that don’t affect water clarity like an algal bloom. They can be found attached to the bottom of the waterway, floating in the water, or washed up on shore.

While not all algae are dangerous, those formed by cyanobacteria, dinoflagellates, and diatoms can create harmful toxins.

On June 11, two harmful algal mats were found in Salmon Creek tributaries, including a location at Horse Meadow campground in the Sequoia National Forest. A mat was also found Monday in the San Joaquin River, just West of Shields Avenue in Fresno County.

The community is advised to avoid swimming and to keep pets from drinking the water in these areas.

Those visiting the Los Banos Creek Reservoir in Merced County are asked to be aware of potential algae and scum based on testing that detected cyanotoxin. Those who fish are also cautioned against eating shellfish from this reservoir.

A map of all reported harmful algal blooms can be found on the State of California Water Quality Monitoring Council website.