The Cahokia Joachim Watershed, also known as HUC 07140101, covers an area of approximately 1,074 square miles in Illinois and Missouri. The watershed is primarily agricultural, with some urban areas. The hydrology of the area is influenced by the Mississippi and Meramec Rivers, which are the main surface water sources for the watershed. The watershed receives an average of 40 inches of precipitation per year, with most of the rainfall occurring in the spring and summer months. Snowfall is typically minimal, with an average of only 9 inches per year. The primary reservoir in the watershed is the Meramec River, which is used for drinking water, recreation, and power generation. In recent years, the area has experienced an increase in extreme weather events, such as floods and droughts, which have had a significant impact on the hydrology and surface water quality of the watershed.