Millions of people across the U.S. flock to beaches and water to escape the summer heat.

Your favorite lake or watering hole may look refreshing and inviting but it may also be a breeding ground for disease. Most types of organisms and algae found in the water are beneficial -- they produce oxygen and food for fish and animals. However germs can thrive when things heat up from the sun.

There have been a handful of reports of contaminated bodies of water in the Pacific Northwest, including Horseshoe Lake in Kitsap County, which was recently closed after a suspected gastrointestinal outbreak from contaminated water.

According to recent a recent report from The Centers for Disease Control and Prevention, disease outbreaks found in recreation water have caused almost 5,000 illnesses and two deaths from 2000 to 2014. The CDC also said that more than 80 percent of outbreaks start between June and August.

The report found that the majority of people got sick when they swallowed water contaminated with feces, pathogens and certain kinds of viruses and bacteria like E.coli, Shigella and the norovirus. The rest of the outbreaks were caused by parasites transmitted by birds, toxins and chemicals or harmful algae blooms. Catching one of these bugs can lead to a list of infections and symptoms including diarrhea, nausea , vomiting, rashes and ear, eye and respiratory infections.

The EPA said water can be polluted by trash such as picnic plates, plastic bags and bottles. But the most frequent source of disease causing organisms are from sewage overflows and malfunctioning septic systems, polluted storm water runoff and boating wastes.

If you choose to swim in untreated water, use caution in areas of water that are shallow, warm, poorly circulating and over-crowded. Swimmers should also steer clear from water that's discolored, smelly, foamy or scummy, and frequented by children with no or limited toileting skills.

The CDC also wants swimmers to do their part to keep their family, friends and the public healthy. Stay out of the water if you are sick or if you have an open wound that is not covered with a waterproof bandage and to do your best to avoid swallowing the water.

According to the EPA your local public health office can tell you if the water in your area is monitored and where the results are posted.

According to the Idaho Department of Health, since January 2010, three reported outbreaks that were definitely associated with untreated recreational water were:

  • Multiple causes, Middle Fork of the Salmon River in 2013, https://healthandwelfare.idaho.gov/Portals/0/Health/Epi/IDB/201406.pdf
  • Norovirus at Eagle Island State Park in 2014, https://parksandrecreation.idaho.gov/news/eagle-island-state-park-illness-identified-norovirus-cdhd-urges-healthy-swimming-habits
  • “Swimmer’s itch”, private lake, in 2015. Swimmer’s itch is a skin rash caused by an allergic reaction to certain parasites. Often not reported to public health agencies.