Recreational Risks from Water-borne Diseases in Iowa Waters

Many different microscopic organisms can be present in lakes and streams that are used for swimming, boating, fishing, and other recreational activities. These organisms include protozoa, bacteria, and viruses that enter the water from human and animal waste. Some of these organisms can make people sick. These are considered pathogens. If people are exposed to these organisms through ingestion or contact with open wounds, they can develop infections, leading to symptoms including stomach aches and diarrhea. Although rare, some of these infections can be fatal. There is currently very little information on how many people contract infectious diseases from recreating in Iowa's waterways, but it is still important to be informed about where and when the risks are highest and to minimize risks by taking precautions, such as showering and washing your hands after touching the water. By monitoring our waterways, Drake University and our partners are helping to find sources of the problem, assess risks, and target clean-up efforts.

Escherichia coli (E. coli) are bacteria that are common in our digestive systems and the digestive systems of many warm-blooded animals. Not all E. coli make us sick. In fact, most E. coli are "commensal," which means they are not disease-causing. If you hear about people getting sick from E. coli at a restaurant, for example, those people have been exposed to a subset of the E. coli family that are pathogenic (disease-causing).

E. coli are relatively cheap, quick, and easy to measure. This has led to E. coli being used as indicators of the risk of getting sick from water-borne diseases. When E. coli are found in the water, it is very likely that human or animal wastes are getting into the water. The higher the concentrations of E. coli in the water, the higher the risks for people.

Studies conducted in other US states have shown a correlation between E. coli levels at beaches and the numbers of people reporting symptomatic illness. These studies led the US Environmental Protection Agency to develop standards for recreational waters. If a waterbody has E. coli levels at the primary recreational standard (for activities that involve complete submersion in water), they are considered to have a 3.6% risk of getting sick. In other words, according to the EPA, your risk of getting sick from swimming in water at the standard is equal to 36 illnesses per 1000 swimming events. Since the chance of ingesting water is lower with activities that do not include a person's head going underwater, it would take higher levels of bacteria in the water to make a person sick. Therefore, the recreational water quality standards for "secondary contact" activities are higher.

Recreational water quality standards for Iowa:

Iowa DNR monitoring the water at public beaches for E. coli throughout the recreation season, from Memorial Day to Labor Day. The water samples are collected early each week and the results are posted each Friday, to help guide decisions for folks recreating over the weekend. If the E. coli levels are above the recreational water standards, warnings will be posted at the beach, but beaches will usually remain open if people are willing to take the risk.

Iowa's streams are not monitored as regularly as beaches, but many streams in Iowa are considered "impaired" because E. coli levels are higher than the standards. In general, E. coli levels are higher in streams because the water is flowing and can carry more mud and other particles. Muddy water also doesn't allow as much sunlight to get in. Ultra-violet rays in sunshine act as a powerful disinfectant. People should be aware that just because a warning is not posted does not mean there is no risk. It is always best to minimize the amount of water that is ingested.

As recreation in Iowa's streams becomes more and more popular, efforts are underway to better understand the risks and determine the causes of fecal pollution. A study conducted by Polk County Conservation, Drake University, and the USDA/USGS Lab for Infectious Diseases in the Environment measured water samples for many different disease-causing organisms over 2 years (2020 and 2021) and calculated average risks for 6 locations around the metro. Here are the results:

The water in rivers is always moving, so the level of risk is always changing. While this study shows us where risks are higher, is not possible to know the exact risk at any given time.

Sources of fecal waste