▁administrative ▁boundary ▁separ ating ▁the ▁two ▁regions ▁does ▁not ▁depend ▁on ▁the ▁course ▁of ▁the ▁river , ▁and ▁is ▁about ▁six ▁kilom eters ▁west ▁of ▁the ▁Mont . ▁ ▁Geography ▁▁ ▁The ▁Cou es non , ▁the ▁S ée ▁and ▁the ▁S él une ▁form ▁part ▁of ▁the ▁complex ▁water ▁system ▁of ▁the ▁bay ▁of ▁Mont ▁Saint - Mich el . ▁On ▁one ▁side , ▁the ▁t ide ▁brings ▁large ▁quantities ▁of ▁sed iment ▁which ▁cause ▁large ▁sand bars ▁within ▁the ▁river . ▁On ▁the ▁other , ▁the ▁three ▁water c ourses ▁drive ▁the ▁sed iment ▁back ▁out ▁to ▁sea . ▁ ▁In ▁the ▁ 2 0 th ▁century , ▁the ▁Cou es non ▁was ▁turned ▁into ▁a ▁canal , ▁to ▁reduce ▁the ▁er os ion ▁of ▁its ▁banks . ▁In ▁ 1 9 6 9 , ▁a ▁dam ▁was ▁built . ▁These ▁modifications , ▁and ▁the ▁cause way ▁linking ▁Mont ▁Saint - Mich el ▁to ▁the ▁main land , ▁have ▁caused ▁the ▁bu il dup ▁of ▁mud fl ats . ▁To ▁prevent ▁the ▁Mont ▁becoming ▁too ▁connected ▁to ▁the ▁main land , ▁plans ▁are ▁in ▁place ▁to ▁replace ▁the ▁cause way ▁with ▁a ▁bridge , ▁and ▁to ▁modify ▁the ▁dam ▁so ▁that ▁the ▁sed iment ▁can ▁once ▁again ▁be ▁driven ▁out ▁to ▁sea . ▁ ▁During ▁spring ▁t ides , ▁a ▁tid al ▁bore ▁— ▁a ▁wave ▁caused ▁by ▁the ▁incoming ▁t ide ▁— ▁can ▁be ▁seen ▁working ▁its ▁way ▁up ▁the ▁river . ▁ ▁The ▁Cou es non ▁flows ▁through ▁the