▁the ▁lake ▁is ▁only ▁about ▁a ▁met re ▁deep ▁on ▁average , ▁very ▁rich ▁water ▁sources ▁and ▁the ▁Hun te ▁itself ▁ensure ▁that ▁its ▁water ▁level ▁is ▁relatively ▁constant . ▁Pre viously ▁these ▁head stream s ▁combined ▁with ▁regular ▁heavy ▁ra inf all ▁to ▁cause ▁flo oding , ▁so ▁that ▁in ▁the ▁ 1 9 4 0 s ▁work ▁began ▁to ▁build ▁dy kes ▁around ▁the ▁lake . ▁In ▁the ▁period ▁ 1 9 4 1 - 1 9 4 5 ▁foreign ▁forced ▁labour ▁was ▁used ▁for ▁this ▁on ▁a ▁large ▁scale . ▁The ▁re clam ation ▁and ▁subsequent ▁lack ▁of ▁annual ▁flo oding ▁resulted ▁in ▁alg ae ▁growing ▁in ▁large ▁quantities ▁in ▁the ▁lake ▁and ▁hence ▁dep riv ing ▁most ▁other ▁organ isms ▁of ▁o xygen . ▁The ▁low ▁water ▁level ▁was ▁caused ▁by ▁heavy ▁sil ting , ▁also ▁a ▁result ▁of ▁dy king ▁the ▁lake . ▁With ▁the ▁help ▁of ▁several ▁lo cks ▁it ▁was ▁possible ▁to ▁control ▁the ▁high ▁water ▁levels ▁artificial ly ▁without ▁greatly ▁inter fer ing ▁with ▁nature . ▁Nevertheless , ▁the ▁D ü m mer ▁suff ers ▁from ▁heavy ▁nut ri ent ▁poll ution ▁caused ▁by ▁int ensive ▁agricult ure . ▁ ▁The ▁remains ▁of ▁New ▁Stone ▁Age ▁settlement s ▁have ▁been ▁found ▁on ▁the ▁sh ores ▁of ▁the ▁D ü m mer . ▁ ▁References ▁ ▁S ources ▁▁ ▁Friedrich , ▁Ernst ▁Andreas ▁( 1 9 8 0 ). ▁Natur den k male ▁Nied ers ach sens . ▁Han over . ▁▁ ▁Hel big , ▁Andreas