The basic strategy used at the 63rd Street Beach is to sample the water at two different points along each of five lines that radiate out from a single spot on the shore, like spokes on a wheel. Researchers also test the waters at the lagoon mouth, harbor mouth, and break walls. The concentration of bacteria in each sample is then compared with water currents and weather conditions, including rainfall and wind speed and direction. When the study winds down in September, researchers hope to have gathered enough data to begin to see patterns, and any correlations observed between E. coli levels and the other factors measured will be used to predict future surges in the level of bacteria. Although this sounds simple enough, predicting levels of E. coli is actually a tricky business.
Rain can raise bacteria levels when storm-water runoff washes sewage into the lake.
But a lack of rain is also problematic, causing lake levels to fall and water temperatures to rise, providing an ideal breeding ground for E. coli. Wind can also raise levels of E. coli as choppy waters churn up bacteria in sediment. Fortunately, people rarely go swimming on days when the waters are rough. The study also helped identify a unique problem at the 63rd Street Beach. The shape of the beach creates a sort of bay that tends to trap bacteria.