NOAA on toxic algae According to NOAA, “The primary culprit in these blooms is excess fertilizer—mostly phosphorous—that washes off agricultural land into rivers and streams that flow into the lake. Microscopic algae populations can explode in numbers when nutrient levels in the water climb. Some species of algae produce toxins that can make lake life as well as people sick.”
here is Ohio EPA’s map of current algae bloom warnings Know before you set out to recreate!
and here is information from the Ohio Department of Health about recognizing toxic algae blooms.