What’s That Lurking on the Lakeshore? E. Coli Takes a Stand on Land


During the first decade and a half of the twenty-first century, contaminated recreation water entered the public concern’s limelight. Last year lake closures due to E. coli contamination sky-rocketed in North America, most notably in the Midwest, affecting major recreational hubs in the Great Lakes region and stretching as far south as the Missouri and Arkansas Ozarks. For areas that generally stay open all year and rarely see the need for concern of bacterial infection, these lakes and streams closed to the public in hopes of reducing E. coli exposure.


Escherichia coli (“E. coli”) is bacteria predominantly found in human and animal fecal matter. The most common strains of E. coli are harmless, living and thriving in the intestines. However, the bacteria are prone to adaptation and can form strains that cause severe illness. The EPA cites 1982 as the first recognition of E. coli as the cause of an outbreak stemming from contaminated hamburger meat.  It wasn’t until 1999 that scientists identified E. coli as a waterborne contaminant in New York and Washington. Since 1999, waterborne E. coli has increased and caused beaches, lakes, streams, and watersheds to either shut down or close off to public recreational use. The Midwest is home to the largest lakes in the United States, and the influx of bacteria provides ample grounds for generally studying the development of E. coli as well as E. coli’s metamorphosis from harmless to dangerous.

Point Source Contamination – Friendly E. coli

E. coli most prominently enters water through “point sources.” Point sources include pipes, ditches, and wells that carry sewage and waste for discharge into water systems. The notion that water could dilute waste substances historically made lakes and especially streams hot spots for dumping. Organic, inorganic, and sewage waste continually cause water quality to decline and provide an atmosphere for optimal bacterial growth. E. coli found in lake and stream waters often indicates the presence of human fecal matter. In the Great Lakes, fecal matter pollution produced a 32% increase in the number of beach advisories and closures in 2003. E. coli presence alone is not the main concern in North American lakes and streams; rather, the type of E. coli and concentration provides area for concern. When the basic strain of E. coli adapts into a more dangerous pathogen, which significantly increases severe illness, humans and animals alike are at risk. However, water environments challenge E. coli’s survival because of the environment’s generally low temperatures, high salinity, and increased solar radiation. Due to these natural constraints on E. coli growth, E. coli that enters water systems via point sources usually contributes to a healthy aquatic ecosystem.

Non-point Sources – Don’t Eat the Sand!

Bacteria flourishing in human and animal intestinal tracks may make it through sewage and waste into the environment. However, studies conducted over the past decade have shown a new trend of contamination. While lake and stream water provide a semi-hostile environment for E. coli to replicate or survive in, these areas are not completely inhospitable. Furthermore, scientists now recognize soil and sand as creating an environment for E. coli to adapt, survive, and flourish, eventually leading to the development of pathogenic strains.

Recently, scientists have discovered that the shallow groundwater below beaches and adjacent to the shoreline harbor elevated levels of E. coli. When E. coli enters the water system, groundwater is often infected as well. The bacteria attach to soil or sand particles and can survive for far longer than free-floating bacteria. Sand protects E. coli from the environmental stresses bacteria experience while in lake or stream water, such as the effects of UV radiation. Sand also allows the bacteria to attach to grains where there is a steady flow of nutrients.  In sum, sand provides the ideal atmosphere for E. coli to survive, adapt, and replicate. Why is this concerning? Tidal washes, run-off, and erosion then transport the preserved and adapted E. coli strains into surface water. The E. coli found in the shallowest parts of lakes and streams resemble the genetic make-up of sand-nourished pathogens and less like the harmless bacteria found at point source locations. The higher concentration of pathogen E. coli creates a much higher risk of contracting a severe illness from the bacteria.

Moreover, in the past decade, with the currently increasing land temperatures, E. coli is surviving the coldest months. While the summer months have always seen an increase in E. coli concentrations, winters typically serve to combat and curb concentrations. Generally, E. coli survives anywhere from two to seven days in water; however, according to a beach contamination study of the Great Lakes, E. coli survived through the winter and tested at high levels in the frozen February sand. This means that come spring thaw, E. coli concentrations start at higher levels, setting up for contamination frenzies and closures all summer.

So, what you’re saying is, I can’t play in the water?

Across the Midwest, recreational lakes, beaches, and streams close every summer to minimize the risk of contracting illnesses due to E. coli exposure. While the prospect of contracting an illness deters most water enthusiasts, some cities, such as Chicago, are making strides in order to reduce general panic. Chicago, for example, is supplying added information to assist visitors to make their own informed decisions. For the past two summers, the Chicago Park District (the “District”) daily posted the E. coli water concentration at select beaches with frequent visitors. The District only closes beach and lake access if the concentration exceeds a certain threshold as mandated by the Environmental Protection Agency. Somewhat concerning, the daily postings do not account for the concentration of E. coli harbored in the sand. On the other hand, Canadian investigations and experiments have found that while some harmful strains of E. coli exist along shorelines and within the shore soil, the majority remains benign, resembling strains of bacteria found in our own bodies.

So, this summer, when there is an E. coli advisory, think about a few things before you swear off swimming, fishing, water skiing, or reading on the beach. Though current research shows increased concentrations of E. coli, higher concentration does not mean that all present strains are pathogenic and cause severe illness upon exposure. Rather, the majority of bacteria found in surface water and in shoreline soil is still categorized as harmless E. coli. While scientists work to find better ways of measuring E. coli concentrations, sources, and prevention, the question remains how safe, or unsafe, recreational lake and stream waters truly are.

The title picture is of Lake Michigan.


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Swimming with E. coli: New efforts to reverse centuries of abuse, The Economist (Jun. 25, 2009), http://www.economist.com/node/13915830.

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