The Milwaukee River Estuary is the natural drainage area of the three watersheds and corresponds to the stream miles designated by the US EPA as the Milwaukee River Estuary Area of Concern (SEWRPC). The Milwaukee River Estuary’s history includes significant modifications to the rivers and estuary stemming from extensive land use modifications from industry, channel dredging for shipping, and flood control features. By changing how the rivers connect with Lake Michigan, these modifications influenced water quality within the Estuary, as well the Estuary’s ability to function naturally. Today, many features of the Milwaukee River Estuary are more similar to the shallow waters of Lake Michigan than traditional river mouths or monitoring locations upstream on the Milwaukee, Menomonee, and Kinnickinnic Rivers. While the area defined as the Milwaukee River Estuary is not actually its own watershed, for the purpose of this analysis, we interpreted the Estuary’s natural drainage area as part of a distinctly unique system. We graded the Estuary separately to remove any bias that its relationship with Lake Michigan would have on our interpretation of each watershed and subwatershed in the Milwaukee River Basin.

The drainage of the Milwaukee River Estuary makes up an area of 16.24 square miles. The streams within that drainage cover the lower 3.1 miles of the Milwaukee River, the lower 3 miles of the Menomonee River, and the lower 2.5 miles of the Kinnickinnic River (US EPA 2017). Land coverage surrounding the Milwaukee River Estuary is approximately 97% urban. The development surrounding the Milwaukee River Estuary is protected from flooding by a nearly continuous series of steel sheet pile levees, which confine the dredged channels of the Milwaukee, Menomonee, and Kinnickinnic Rivers. This design is maintained to make the channels of the Milwaukee River Estuary more accessible for shipping, supporting one of Milwaukee’s oldest industries, as well as to provide flood protection for adjacent development. Though the mouths of large river basins are generally defined by large deposits of sediment, and consistent flooding during precipitation events (Vannote et al. 1980), the Milwaukee River Estuary has been historically dredged to maintain a specific depth and is cut off from adjacent floodplains by steel walls, making it largely immune to flood events (with historic lake levels). As a result, many features of the Milwaukee River Estuary are more similar to near shore areas of Lake Michigan. On any given day, water can be readily exchanged in either direction between our rivers and Lake Michigan.