Although still open, both Marion Reservoir and Marion County Lake will continue under blue-green algae advisories through July 20.
The advisory level for the county lake, which had been under a less-significant watch, was elevated Thursday to a warning.
Meanwhile, the advisory level at the federal reservoir was lessened to just a watch for the first time this summer.
Blue-green algae warnings are updated each Thursday afternoon and remain in effect until the following Thursday.
Camping sites will remain available, and boat ramps will be open. However, beaches at the county lake will be closed, and direct contact with water via swimming or skiing will be discouraged both places.
Anglers should limit water contact and thoroughly wash hands and arms in clean water after fishing or handling fish. Fillets are safe to eat if rinsed, but heads and organs should be discarded.
Public water supplies for Marion, Hillsboro, and Peabody all use Marion Reservoir as their source. However, treatment procedures were changed several years ago to make municipal water safe to consume even during algae blooms.
Blooms develop rapidly and may float around a lake. If there is scum or a paint-like surface, or the water appears bright green, a harmful bloom may be present.
Blue-green algae, technically known as cyanobacteria, come in several varieties, most of which release toxins when they die.
With some species, the toxins are mild irritants. With others, they are potentially fatal neurotoxins. The exact species in any bloom cannot immediately be determined.
While no humans have died in Kansas during blue-green algae blooms, many dogs have died, and human illnesses have been reported.
Symptoms in humans include sore throat, congestion, cough, wheezing, difficulty breathing, itchy or red skin, blistering, hives or other rashes, earache, agitation, headache, abdominal pain, diarrhea, vomiting, and eye irritation.