The natural beauty of northern Wisconsin and Michigan’s Upper Peninsula would seem to make it the last place to have to worry about clean water in lakes and rivers.

Yet even here, unfortunately, people need to be cautious about when and where they choose to go into the water — especially this summer, with its frequent heavy rains, experts say.

Can you trust any area waterway? Experts advise no.

Bacteria, viruses and parasites can be carried by runoff from wildlife, agriculture or other human activities — think overwhelmed septic systems — into seemingly clear waters where people go to swim or otherwise use for recreation.

Thousands annually become ill coming into contact with these waterborne agents, according to the Health and Human Services Department in Wisconsin’s Marinette County.

The good news is most of the dangerous elements from waste or runoff diminish to more normal levels two to three days after a heavy rain, Marinette County officials advised.

Flooded lakes may also contain other hazards to swimmers and boaters, such as submerged docks and storm debris and chemical contamination from spills or damaged boats.

Heavy rains may also trigger an algae bloom, which in turn can cause rashes, diarrhea or respiratory issues for humans or pets.

When in doubt, stay out. If the waterway looks or smells differently than normal, wait until it returns to normal state.

Other advice from Marinette County on safe swimming includes:

•Avoid swimming after a heavy rain.

•Supervise children closely. Strongly encourage them not to swallow water and avoid excessive splashing and rough playing in the water.

•Look for trash and other signs of pollution such as oil slicks in the water. These kinds of pollutants may indicate the presence of disease-causing microorganisms.

•Do not swallow water or submerge your head.

•Do not go swimming if you have open wounds or had recent piercings or surgery.

•Never swim alone. Have a designated adult watch over the children.

•Shower after swimming in any body of water.

•People with weakened immune systems, infants and pregnant women should avoid swimming in untreated waters.

•Contact your doctor if you feel ill after swimming.