The Witham Navigable Drains are located in Lincolnshire, England, and are part of a much larger drainage system managed by the Witham Fourth District Internal Drainage Board. The Witham Fourth District comprises the East Fen and West Fen, to the north of Boston, which together cover an area of 97 square miles (250 km2). In total there are over 438 miles (705 km) of drainage ditches, of which under 60 miles (97 km) are navigable. Navigation is normally only possible in the summer months, as the drains are maintained at a lower level in winter, and are subject to sudden changes in level as a result of their primary drainage function, which can leave boats stranded. Access to the drains is from the River Witham at Anton's Gowt Lock.