The St. Louis River, the largest U.S. tributary to Lake Superior, drains 3,634 square miles, entering the southwestern corner of the lake between Duluth, MN and Superior, WI. The river flows 179 miles through three distinct areas; coarse soils, glacial till and outwash deposits at its headwaters; a deep narrow gorge at Jay Cooke State Park; and red clay deposits at its lower reaches. As the river approaches Duluth and Superior it takes on the characteristics of a 12,000 acre (4856 hectare) freshwater estuary. While the upper part of the estuary has some wilderness-like qualities, the lower portion is decidedly urban. The RUSS will be located in this lower urban portion.

The lower St. Louis River is one of 42 Areas of Concern (AOC) in the Lake Superior basin. An AOC is a site that has serious environmental pollution problems that require remedial action and the development of a Remedial Action Plan (RAP) to outline ways to restore the area. See EPA GLNPO for more information on the Great Lakes AOCs. The Minnesota Pollution Control Agency has a web page that discusses contaminated sediments within the St Louis River.

A large publically owned wastewater treatment plant (Western Lake Superior Sanitary District, WLSSD) discharges below the potential RUSS site and the river carries a heavy load of suspended sediments from non-point sources. The river also has a number of sites known to contain contaminated sediments.

The lower St Louis provides good fish habitat and is an excellent warm water fishery. However, the recent invasion of exotic fish (Eurasian ruffe and round goby) may threaten native fish populations (see MN Sea Grant exotic species ).