The Great Lakes are the largest surface freshwater system on Earth, with a basin that is home to approximately 30 million people (USEPA, 2015) . Lake Michigan is the only one of the Great Lakes that lies entirely within the United States, with a maximum length of 307 miles and a maximum width of 118 miles. Lake Michigan's shoreline, composed mostly of sand and pebble beaches, extends for 1,640 miles along the coasts of Illinois, Indiana, Michigan, and Wisconsin, as well as some islands (NOAA, 2015a). The Illinois portion of the Lake Michigan watershed (Figure 1) is only 100 square miles (0.22% of the total lake area), and the state's shoreline borders the lake for a short 63 miles (IEPA, 2014). However, despite this relatively small area of ​​Lake Michigan, half of the state's population lives within the watershed. Recreational water activities are popular throughout the Great Lakes and along Illinois' Lake Michigan coast. Lake Michigan is Illinois' largest recreational resource, as well as the state's largest drinking water supply and a major economic benefit (IEPA, 2014). With so many people engaged in water-based activities, which in turn affect and are affected by the lake, it is important to monitor the lake frequently for potential health risks. Increased efforts have been made to protect human health from contaminated water during recreational activities. , especially swimming. For many years, waters have been tested for certain types of fecal indicator bacteria (FIB), bacteria commonly found in human and animal feces. While FIB generally does not cause human disease, FIB in water may indicate the presence of feces and associated pathogenic bacteria, viruses, and protozoa – organisms and agents that have also been found… middle of paper…. ..s in Cook County and Lake County may be similarly affected, as the EPA has determined that the entire Lake Michigan shoreline in Illinois is free of CSO communities (USEPA, 2007). Numerous studies have looked at various weather variables and environmental conditions and have found some associated with higher or lower densities of E. coli and other bacteria in the water. There are 10 major meteorological variables included for investigation in this study that provide a detailed description of the climate and conditions of the lake where E was sampled. coli. These 10 variables are atmospheric pressure, air temperature, dew point, precipitation, relative humidity, solar radiation (insolation), water temperature, wave height, wind speed and wind direction. From a meteorological point of view, some of these variables are closely related and influence each other.