The River Witham is a river almost entirely in the county of Lincolnshire in the east of England. It rises south of Grantham close to South Witham at SK8818, passes through the centre of Grantham (where it may be closely followed using the Riverside Walk through Wyndham Park and Queen Elizabeth Park), passes Lincoln at SK9771 and at Boston, TF3244, flows into The Haven, a tidal arm of The Wash, near RSPB Frampton Marsh.