The Upper Illinois Watershed (HUC 07120005) encompasses about 4,473 square miles in northern Illinois and southern Wisconsin. The hydrology of the watershed is influenced by the Des Plaines River, which flows through the region, and the Fox River, which joins the Des Plaines River in the watershed. During winter months, the region receives an average snowfall of 36 inches, which can contribute to increased surface water runoff during spring months. The watershed contains several reservoirs, including the Fox River Chain O'Lakes, which serves as a popular recreational area. Recent studies have shown elevated levels of nutrients and sediment in the surface water of the watershed, resulting in poor water quality. Climate trends in the region show a trend towards warmer temperatures and increased precipitation, which may impact hydrology and water quality in the future.