A new alert was issued Friday at Willow Creek Reservoir in Pierce County, while an alert continues at Rockford Lake in Gage County.
The alerts were issued following tests of the lakes' water, in which too much microcystin was found. Microcystin is a toxin released by certain strains of blue-green algae.
Symptoms of exposure to the toxin include rash and blisters, headaches, nausea and muscular pain.
Signs have been posted at the lakes, urging people and pets to stay out of the water. People can still use the lakes' public areas for other activities.
The alerts will continue at the lakes until at least two weeks of readings are below the alert threshold.