Ohio public health officials have elevated the public health advisory for Grand Lake St. Marys as a result of increased levels of microcystin toxin in the 13,500-acre lake along with the probable case of a person getting sick after recreating on the lake.
Signs have been posted on Grand Lake public beaches and boat ramps recommending that visitors and pets avoid swimming and wading in the lake. Boaters and jet-skiers are encouraged to understand the risks of exposure to higher levels of microsytin, especially if the lake shows scum, slime or resembles spilled paint. 
Microcystin is a toxic chemical produced by cyanobacteria (often called blue-green algae) which cause harmful algal blooms (HABs).  HABs can occur in lakes, ponds and slow-moving rivers when there are warm temperatures, sunlight, and excessive amounts of nutrients (phosphorus and nitrogen) in the water.  Some HABs are visible as thick mats or scum on the surface of the water which can vary in color, including bluish-green, bright green, or even red or maroon.
“We are seeing high levels of microcystin that are likely the result of record rainfall this year,” said Craig Butler, director of the Ohio Environmental Protection Agency. 
Microcystin levels at Grand Lake St. Marys State Park beaches recently ranged from 63.4 micrograms per cubic liter (µg/L), sometimes expressed as parts per billion, to 99.6 µg/L.  According to the World Health Organization, there is a high relative probability of acute health effects during recreational exposure to microcystin in contaminated water beginning at 20 µg/L.
Swallowing or coming into contact with water containing high levels of microcystin can make people sick, including but not limited to rashes, hives, skin blisters and runny nose to severe diarrhea, vomiting, weakness, dizziness, abnormal liver function and difficulty breathing.  The most common ways individuals come into contact with HABs during water recreational activities include accidental swallowing of contaminated water while swimming; skin contact through swimming or wading; and breathing in aerosolized water droplets (misting) while power boating, jet skiing, water skiing or tubing.
“A local health department notified us of a visitor to Grand Lake who developed an illness after recreating on the lake,” said Mary DiOrio, M.D., medical director of the Ohio Department of Health.  “After a public health investigation, it was determined that the illness met the criteria as a probable illness due to HAB exposure so we do not believe the lake is healthy for swimming or wading.”
Individuals who have questions about this public health advisory can call the ODH Public Information Line between 8 a.m. and 5 p.m. seven days a week at 1-866-800-1404. The Ohio EPA maintains a website (www.ohioalgaeinfo.com) with information and resources about algae information in Ohio recreational waters. The ODH website (www.odh.ohio.gov) also contains HAB information.
Each week during spring and summer months, the Ohio Department of Natural Resources and Ohio EPA tests water at Grand Lake and other select public inland lakes and shares the results with ODH.  The data are used to help determine when public health advisories are necessary.  Ohio will continue testing Grand Lake waters, while reviewing its protocols and strategies to ensure that it has the best measures in place to determine when to adjust advisory levels.
Over the past five years, Ohio has spent more than $25 million to improve the water quality of Grand Lake St. Marys and the surrounding region through improved nutrient reduction policies such as constructing wetlands and drainage control devices, removing fish such as carp that contribute to HABs, dredging the lake to remove nutrient-rich sediment and algae, and installing water quality monitoring devices to study the impact of the phosphorous to both the lake and the region.