Summer is a perfect time to swim in lakes and rivers. But before you jump into the water, be aware of what may lurk below. Certain bacteria and parasites in lakes and rivers can make you sick.

“Many of these bacteria or parasites are not visible in the water,” said Julie Carriveau, an infection prevention nurse at Marshfield Clinic. “So you really have to be careful with trying not to swallow water and what to do after being in the water.”

Children, the elderly and people with immune-compromising conditions are more likely to become sick from these types of pathogens, but everyone can be affected. Animals also can be affected.

Carriveau says people should be aware of three main illness-causing agents found in streams, lakes and rivers.

Related Shine365 summer swimming posts:

Debunking swimming safety myths

Water safety in lakes, rivers and streams

How to ditch swimmer’s itch