[4] Of all tributaries of the Kishwaukee, the South Branch is the largest in terms of the area drained.

[4] The South Branch flows through DeKalb County, Illinois,[6] draining 441 square miles (1,142 km2) of land area.

[4] Part of the South Branch's river bed is the plain of an ancient lake.

[6] The assessment looked at overall resource quality and determined the factors responsible for lower quality conditions were "nutrients and organic enrichment (low dissolved oxygen) from agriculture and municipal point source pollution.

[9] Numerous roads and bridges were closed, and the cities of DeKalb and Sycamore declared local emergencies.