The germs found in water usually come from human or animal feces; rainwater picks up the feces and then drains into swimming areas. Contaminated water can make people sick if they swallow it and cause infections if it comes in contact with an open cut. Luckily, there are ways to avoid problems.
First, if you’re heading to a lake or beach, check online to see if a swim area has any warnings or closures, especially after a rainstorm. If you have health issues, especially with conditions that compromise your immune system, check with a healthcare provider before swimming in natural bodies of water.
Be sure to stay out of water if the swim area is closed, if the water looks discolored or foggier than usual, the water has an odor, or if pipes are spilling into the water. Also avoid swimming if you have diarrhea, or you have an open cut or wound.
Once you are swimming, do not swallow the water, keep sand away from your mouth and do not use the bathroom in the water.