today, commercial traffic, apart from tour boats, has ceased above the port of boston (the haven) and only pleasure craft carry on through the lock at the grand sluice into the witham. although the lock is only long, it is possible for longer boats to pass through it at certain states of the tide. unlike many such sea locks, the reverse-facing gates close on every tide, as the normal high tide water level is higher than the level of the river, while at low tides there is insufficient water in the haven to allow exit from the lock. passage is therefore restricted to a brief period approximately two hours before or after high water. it is still possible to navigate many of the drains in small vessels, and a new lock, completed in december 2008, provides entry to the south forty-foot drain from below the grand sluice so that vessels will be able to reach the fens without venturing out to the wash, as part of the fens waterways link.