retention basin

English Thesaurus

1. a storage site similar to a detention basin but the water in storage is permanently obstructed from flowing downstream (noun.location)

hypernym	:	basin, catchment area, catchment basin, drainage area, drainage basin, river basin, watershed,
definition	:	the entire geographical area drained by a river and its tributaries; an area characterized by all runoff being conveyed to the same outlet (noun.location)