Seven of the 21 reported illnesses linked to Grand Lake St. Marys’ algal toxins are probably lake-related, the Ohio Dept. of Health says. 

From the Daily Standard:

"…The six males and one female range in age from 6 to 79 years old, according to data released late Wednesday by Jen House of the Ohio Department of Health (ODH). The names of the victims were not released, however, none of the cases are considered life-threatening, House said.

The state’s health department received 21 reports of illnesses linked to the lake. Of those, seven were labeled probable; four are still being investigated; and 10 have been ruled not a case. No confirmed cases exist at this time, House said.
"Cases are interviewed and classified based on the strength of evidence by comparing information on the case to the CDC (Centers for Disease Control and Prevention) proposed case definitions," she explained.
House said the seven "probable" cases met criteria for a suspect case and laboratory documentation exists of a harmful algae toxin in the lake water. The cases involve three people from Mercer County and one each from Auglaize, Shelby, Allen and Montgomery counties, she said.

Symptoms reported by those who became ill include headaches, rashes and diarrhea, health officials said."