The river takes its name from the dark brown color of its water, which is caused by suspended sediments and organic materials picked up along its course.

The Black River watershed encompasses 287 square miles (740 km2) across two counties and 13 townships.

The Middle Branch Black River is formed by the junction of the Little Bear Lake Drain and Melvin Creek at 42°25′04″N 86°15′01″W / 42.41778°N 86.25028°W / 42.41778; -86.25028 (Middle Branch Black River (source))[5] in southern Lee Township, near the boundary with Van Buren County.

[4] About three miles above its mouth on Lake Michigan, the river forks, with the South Branch draining Van Buren County.

Less than three miles further upstream, the river forks again into the Middle and North Branches.