The River Witham starts, briefly, in Leicestershire from thereon in is entirely within Lincolnshire. The Upper Witham Catchment starts from just south of Grantham to Stamp End Sluice in Lincoln. The River Brant and River Till are within this operational catchment. The River Till drains land to the east of Gainsborough. The Fossdyke Canal provides a navigable link from the River Trent to the River Witham. The Lower Witham Catchment has seven separate sub catchments, two of which are below the tidal limit and begins at the Stamp End sluice in Lincoln and flows to the tidal limit at Grand Sluice in Boston. The major tributaries of the Lower Witham include the Barlings Eau, River Bain, and River Slea.
The Limestone Becks are a group of spring fed streams within the Witham catchment that result from the limestone aquifer which runs through western Lincolnshire. The Becks have unique features including the Tufa waterfalls which only form in calcium rich conditions. Historically, the Becks were surrounded by wet meadows but today they have mostly been straightened and suffer from low flow, invasive species, and poorly maintained habitats.
To the east of the Steeping and Eaus Catchment the Lincolnshire Wolds Area of Outstanding Natural Beauty (AONB) dominates the landscape. Chalk streams rise from the chalk outcrop in this catchment. Further east the catchment becomes coastal floodplain and the watercourses flow to the North Sea. The South Forty Foot Catchment also known as the Black Sluice Navigation takes water from the fenland area of South Lincolnshire into the Boston Haven at the Black Sluice. The East and West Fens Catchment intercepts water from the higher ground before discharging it down drains into the Haven at Boston. The Witham Drains are historic network of channels that drain the low-lying fenland areas and supply water for irrigation in summer months.