rain age ▁system ▁managed ▁by ▁the ▁With am ▁Four th ▁District ▁In ternal ▁D rain age ▁Board . ▁The ▁With am ▁Four th ▁District ▁compr ises ▁the ▁East ▁Fen ▁and ▁West ▁Fen , ▁to ▁the ▁north ▁of ▁Boston , ▁which ▁together ▁cover ▁an ▁area ▁of ▁. ▁In ▁total ▁there ▁are ▁over ▁ ▁of ▁d rain age ▁d itch es , ▁of ▁which ▁under ▁ ▁are ▁navig able . ▁Navigation ▁is ▁normally ▁only ▁possible ▁in ▁the ▁summer ▁months , ▁as ▁the ▁dra ins ▁are ▁maintained ▁at ▁a ▁lower ▁level ▁in ▁winter , ▁and ▁are ▁subject ▁to ▁sudden ▁changes ▁in ▁level ▁as ▁a ▁result ▁of ▁their ▁primary ▁d rain age ▁function , ▁which ▁can ▁leave ▁boats ▁str and ed . ▁Access ▁to ▁the ▁dra ins ▁is ▁from ▁the ▁River ▁With am ▁at ▁Anton ' s ▁G ow t ▁Lock . ▁ ▁The ▁area ▁is ▁bounded ▁by ▁the ▁River ▁With am ▁to ▁the ▁south ▁and ▁west , ▁and ▁the ▁Ste eping ▁River ▁to ▁the ▁north . ▁Since ▁the ▁ 1 1 th ▁century , ▁there ▁have ▁been ▁attempts ▁to ▁prevent ▁the ▁f ens ▁from ▁flo oding , ▁so ▁that ▁they ▁could ▁be ▁used ▁for ▁agricult ure . ▁A ▁major ▁advance ▁was ▁made ▁in ▁the ▁sevent e enth ▁century , ▁when ▁Advent ur ers ▁built ▁dra ins ▁in ▁return ▁for ▁rights ▁to ▁some ▁of ▁the ▁rec laimed ▁land , ▁but ▁the ▁success ▁was ▁short - l ived , ▁as ▁Fen men ▁and ▁Common ers ▁ri oted ▁in ▁ 1 6 4 2 ▁and ▁destroyed ▁the ▁works .