The River Bain is a river in Lincolnshire, England, and a tributary of the River Witham. The Bain rises in the Lincolnshire Wolds at Ludford, a village on The Viking Way long-distance footpath, and flows through or past the villages of Burgh on Bain, Biscathorpe, Donington on Bain, Goulceby with Asterby and Hemingby before reaching the town of Horncastle where it is joined by the River Waring, which rises at Belchford, 5 miles (8.0 km) to the north east of Horncastle.