The St. Louis River is the largest tributary to Lake Superior in Minnesota. It drains a predominantly forested area of about 3,650 mi² (Minnesota Department of Conservation, 1959) and discharges into the lake at Duluth.

The Mesabi Iron Range, noted for rich deposits of iron ore, parallels much of the northern watershed boundary. Large areas of land were altered by mining activities, as seen on the Landsat-1 MSS 7 images for September 26, 19744 (No. 1795-16203). The northeastward-trending string of water bodies along the northern boundary are flooded mine pits and tailings basins. The northeastern part of the watershed is largely State and National forest, whereas much of the southwestern and central parts are peat-covered wetlands.

Generalized topographic features are shown on the map above. The topographic high along the northern boundary includes the Iron Range and is dissected by post-glacial drainage. The most notable drainage gap is that occupied by the Embarrass River. The series of southwestward-trending elongate hills in the eastern part of the watershed, visible on both the Landsat image and the topographic map, is the Toimi Drumlin Field (Wright, 1972). Topographically low, relatively flat land in the southwestern and central parts is a glacial lake plain. St. Louis River gradients are highly variable, being 9 ft/mi from its headwaters to the mouth of Partridge River, slightly more than 1 ft/mi from Partridge River to Cloquet, and 35 to 40 ft/mi in a 15-mi reach below Cloquest.

The watershed is sparsely settled except for its northern and south-eastern parts. About 80 percent of the urban population lives on the Iron Range. Most of the suburban and rural residents alro live on or near the range or in the southeastern part of the watershed. Total population (1970), exclusive of those in the city of Duluth, which is included in the Lake Superior watershed (Olcott and others, 1976), was about 117,000.