The DuPage River, consisting of the East and West Branches as well as the mainstem Lower DuPage, is the largest tributary to the Des Plaines River Basin, covering 353 square miles. The Lower DuPage River watershed covers 168 square miles and encompasses portions of 13 municipalities. The majority of the watershed is within Will County, although portions of the watershed are also in DuPage, Grundy, and Kendall Counties. There are 166 stream miles within the watershed.
This watershed is unique in that it is not a true headwater stream; the Lower DuPage begins at the joining of two other rivers. The Upper DuPage River watershed, that of the East and West Branches combined, is highly urbanized and therefore exerts great influence over the downstream water quality of the Lower DuPage. The watershed is also unique in that the Illinois Environmental Protection Agency (IEPA) includes a portion of the Illinois and Michigan Canal, a manmade canal originally built for the transport of goods from Lake Michigan to the Mississippi River, as a part of the watershed.
The Lower DuPage River begins at the confluence of the East and West Branches DuPage River, at the border of DuPage and Wheatland Townships on public properties owned by the Naperville Park District and the Forest Preserve District of Will County, called the DuPage River Confluence Preserve. The river travels southwest through portions of Naperville and Bolingbrook before joining with Spring Brook east of Plainfield Naperville Road and north of Boughton Road in Naperville. The Lily Cache is another major tributary of the Lower DuPage, originating in Darien and Woodridge and flowing southwest through Bolingbrook and Plainfield before meeting the main stem in Joliet, north of Caton Farm Road and west of Interstate 55. Mink Creek is a tributary located in the middle section of the watershed, originating in unincorporated Will County, flowing through portions of Romeoville and Rockdale before flowing into the Lily Cache in Plainfield, north of Joliet Road (Route 30) and west of Interstate 55.
Rock Run Creek is the tributary south of Mink Creek, originates in Crest Hill and flows southwest through Joliet and unincorporated Will County before meeting the Illinois and Michigan Canal, south of Mound Road and east of Interstate 55 in unincorporated Will County. The portion of the Illinois and Michigan Canal that is within the Lower DuPage River watershed originates where the Canal separates from the Des Plaines River in Joliet, east of Brandon Road and south of Railroad Street (Route 6) and follows southwest through portions of Joliet, Channahon and unincorporated Will County before flowing into the main stem.
South of where the Lily Cache flows into the main stem, the river flows south through portions of Joliet, Shorewood, Channahon, Minooka and unincorporated Will County before flowing into the Des Plaines River north of Walnut Lane and east of the Illinois and Michigan Canal Trail near the border of Kendall and Will Counties in the Illinois Department of Natural Resources’ (IDNR) Illinois and Michigan Canal State Park. The Channahon Dam is located 0.5 miles upstream from the confluence. Another dam within the watershed is the Hammel Woods Dam in the Hammel Woods Forest Preserve in Shorewood.