1 8 1 8 , ▁and ▁would ▁continue ▁until ▁ 1 8 2 1 . ▁Cot ting ▁died ▁two ▁years ▁prior ▁to ▁the ▁dam ' s ▁completion ▁in ▁ 1 8 1 9 . ▁Con struct ed ▁from ▁stone , ▁one ▁arm ▁of ▁the ▁dam ▁was ▁built ▁from ▁the ▁foot ▁of ▁Be acon ▁Hill ▁to ▁S ew ell ' s ▁Point ▁( now ▁Ken more ▁Square ) ▁in ▁Brook line . ▁A ▁second ▁cross - dam ▁was ▁constructed ▁from ▁Gra vel ly ▁Point ▁in ▁Ro x bury , ▁div iding ▁Back ▁Bay ▁into ▁two ▁bas ins ▁of ▁ 6 0 0 ▁combined ▁acres . ▁At ▁high ▁t ide ▁the ▁waters ▁of ▁the ▁Charles ▁River ▁would ▁enter ▁the ▁w ester ly ▁bas in , ▁pass ▁through ▁channels ▁to ▁generate ▁tur bine ▁power , ▁and ▁then ▁empty ▁back ▁into ▁the ▁Charles ▁at ▁low ▁t ide . ▁ ▁Fail ure ▁and ▁after math ▁▁ ▁The ▁mil ld am ▁project ▁is ▁regarded ▁as ▁a ▁failure . ▁ ▁Const ruction ▁ran ▁significantly ▁over ▁budget , ▁cost ing ▁nearly ▁$ 7 0 0 , 0 0 0 ▁instead ▁of ▁the ▁proposed ▁$ 2 5 0 , 0 0 0 . ▁Only ▁three ▁fact ories ▁would ▁become ▁established ▁along ▁Boston ' s ▁waters ▁instead ▁of ▁the ▁predicted ▁ 8 1 . ▁Pol l ution ▁also ▁became ▁a ▁problem ▁immediately ▁after ▁the ▁construction ▁of ▁the ▁Mil ld am . ▁En clos ing ▁the ▁dam ▁led ▁to ▁st agn ant ▁and ▁f oul ▁water , ▁precip it ating ▁several ▁compla ints ▁by