The Haven is the tidal river of the port of Boston, Lincolnshire in England. It provides access for shipping between Boston Deeps in The Wash and the town, particularly, the dock. It also serves as the outfall into the sea, of the River Witham and of several major land drains of the northern Fens of eastern England, which are known collectively as the Witham Navigable Drains..

The Fens or Fenlands in eastern England are a naturally marshy region supporting a rich ecology and numerous species. Most of the fens were drained centuries ago, resulting in a flat, dry, low-lying agricultural region supported by a system of drainage channels and man-made rivers and automated pumping stations. There have been unintended consequences to this reclamation, as the land level has continued to sink and the dykes have been built higher to protect it from flooding.