The Fossdyke Navigation runs from Torksey Lock, which joins the tidal river Trent to Lincoln High Bridge, where the Fossdyke Navigation joins the Witham Navigation, which then runs to Grand Sluice Lock at Boston, which is tidal, and thereafter the river runs into the Wash at the outlet of Hobhole Drain. The Witham Navigation has junctions with the Sleaford Navigation (junction at Chapel Hill), Horncastle Navigation (derelict but restoration proposed), the Witham Navigable Drains (junction at Anton's Gowt), with Black Sluice Drain (below Grand Sluice Lock, on the tidal section) and with a number of other small drains and river sections that are navigable or once were.
The Fossdyke Navigation is 11.3 miles (18.1 km) long and has one lock. The Witham Navigation is 36.5 miles (58.7 km), of which 4.3 miles (6.9 km) is tidal below Grand Sluice Lock; the Navigation has three locks.
The maximum size of boat that can navigate both Waterways is
length: 66' 3" (20.2 metres) - Stamp End Lock (longer narrow boats can fit diagonally)
beam: 15' 3" (4.64 metres) - Torksey Lock
height: 11' 3" (3.43 metres) - Saxilby Railway Bridge
draught: 5' 0" (1.52 metres) - cill of Torksey Lock, and cill of Stamp End Lock
Boats wishing to go further down the Witham Navigation from Lincoln Brayford Pool need to have a maximum height of 2.8 metres for the Glory Hole (old Roman Bridge) in Lincoln.
Grand Sluice Lock is only just over 45' (13.7m) long, so boats over this length need to take advantage of the tidal and retained sections of the river Witham becoming level twice on each tide.