E. Coli and Ohio Street Beach

If you swim at Ohio Street Beach, chances are you have had to postpone some of your recent workouts due to elevated levels of E. coli bacteria. I’ve always thought that this was due to the warmer temperatures and stagnant water conditions at that particular beach. And I was partly right. These factors do contribute towards higher E. coli levels. However, the real causes of E. coli contamination may surprise many of you.

So let’s take a closer look…

What exactly is E. coli?

Escherichia coli (E. coli) is a common bacterium that lives in the lower intestinal tract of warm-blooded animals such as humans, mammals, and birds. Most of the hundreds of strains of E. coli are harmless. But they can cause mild to moderate illnesses in humans if consumed in exceedingly high numbers.

How does E. coli enter Lake Michigan?

E. coli can enter Lake Michigan instantaneously from organisms (think seagulls, beach dogs) who void their feces directly into the water. It can also enter the lake indirectly through sewage treatment plant effluent and stormwater runoff.

So there is raw sewage being pumped into the lake right now?

Not usually. Although at one time this was quite a common occurrence. To effectively answer this question, a little history lesson is in order.

Prior to 1975, the majority of the municipalities in Cook County had combined sewer systems that carried both both sanitary sewage and stormwater. During heavy storms and wet-weather periods, these combined systems would often exceed capacity due to the increased amounts of stormwater. The result would be a discharge of sewage directly into Lake Michigan (bad), or a discharge of sewage directly into the neighborhood streets via the manholes (worse).

The design and construction of the Tunnel and Reservoir Plan (a.k.a. “Deep Tunnel”) brought a reprieve from these unpleasantries. There are now 109 miles of tunnels underneath the Chicago metro area that collect the sewage and stormwater flows and route them to surface reservoirs such as quarries for storage until they can be safely treated and discharged.

So how do Chicago’s beaches get contaminated with E. coli?

As noted previously, E.coli enters the lake from direct animal fecal discharge as well as from sewage/stormwater spillovers. The problem is that both of these sources increase significantly during the summer months. For one thing, there are more wild and domestic animals “releasing their payloads” into the lake during the warmer times of the year. Second, there are more wet-weather periods that, on occasion, will produce precipitation levels that simply overwhelm the current capacity of the Deep Tunnel system.

When this happens, the excess stormwater flows back into the Chicago River which can become so swollen with runoff that its water level exceeds that of the lake. Under these circumstances, the Metropolitan Water Reclamation District will open one or more “locks” to prevent flooding. This allows the sewage/stormwater overflow to pour into the lake, thus raising the overall E. coli levels.

What is it about Ohio Street Beach that makes it more prone to higher levels of E. coli?

There are a number of factors that can contribute to elevated E. coli levels at that particular site. First, the area is mostly enclosed by a breakwater that’s designed to keep the water calmer for boats and beach goers. However, it also reduces overall water circulation which can result in more stagnant water conditions.

Second, despite being a smaller beach, Ohio Street Beach gets a lot of visitors of all types. Besides the swimmers and beachgoers, you have the spillover crowds from Navy Pier. Plus you have the masses of anchored boats that hang out in the “Playpen” area not too far offshore. And bigger crowds typically generate more garbage – and more fecal contamination (see comments for yucky details).

Third, Ohio Street Beach is quite isolated compared with other Chicago beaches. Instead of being an open air beach with lots of direct sunlight, it’s mostly surrounded by a number of tall buildings that block out the sunlight for much of the day.

And sunlight is very important for regulating E. coli levels.

In 2003, the American Society for Microbiology conducted a study of Lake Michigan E. coli levels and came up with the following conclusion:

Of these factors, incoming solar radiation (insolation) is arguably the most potent in the inactivation or killing of E. coli and enterococci in water .

And finally, the Chicago Harbor Lock – one of the aforementioned locks that occasionally empties contaminated water into the lake – is located just on the other side of Navy Pier at the mouth of the Chicago River.

See you at Ladder #1!