Monitoring E. coli in a changing beachscape

Abstract Increased emphasis on protection of recreational water quality has led to extensive use of fecal indicator bacteria monitoring of coastal swimming waters in recent years, allowing for long-term, widespread retrospective studies. These studies are especially important for tracking environmental changes and perturbations in regional waters. We show that E. coli concentrations (EC) have decreased in Lake Michigan over the last 15 years, coincident with the rapid invasion of Eurasian quagga mussels (Dreissenidae). While median water clarity in Lake Michigan increased by 32% from 2000 to 2014, median EC decreased by 34.9%. Of the 45 Lake Michigan beaches studied, 42 (93.3%) showed a relative decrease (76% significantly, p E. coli between pre- and post-2007. As a result, Lake Michigan beach advisory frequency decreased by 40.0% ( p p E. coli densities in Lake Michigan. The trends and explanatory factors reported here may have important public health, management and ecological implications.