INDIANAPOLIS -- A toxin from blue-green algae present in Geist Reservoir has prompted state health officials to advise people to take precautions during recreational activity at the reservoir.

State health officials said testing of water samples collected by Veolia Water showed a low level of the toxin in the water. The Indianapolis water supply comes from Geist.

Water company officials said the toxin is removed from drinking water through treatment, but health officials warned that it could cause problems for people swimming, jet skiing or tubing at Geist.

Specifically, health officials said people could get sick from swallowing large amounts of untreated water.

"We recommend avoiding swimming in Geist Reservoir and being careful not to swallow water when skiing or boating," said Dr. Robert Declaw, an epidemiologist with the Indiana Department of Health

Swallowing water contaminated by the toxin can cause abdominal cramps, nausea and diarrhea, health officials said.

In rare cases, liver damage can be caused by drinking the algae toxin. The elderly, young children and people with weak immune systems are most susceptible to the problem.

The toxin can also cause skin rashes, officials said.

"Anyone who comes into contact with untreated water from Geist Reservoir should wash thoroughly with fresh water and soap as soon as possible," Teclaw said.

The Indiana Department of Natural Resources said the toxin does not adversely affect the fish supply and that fish caught at Geist can still be eaten.