. ▁ ▁Over ▁the ▁course ▁of ▁time ▁the ▁mouth ▁of ▁the ▁O ude ▁R ijn ▁s ilt ed ▁up . ▁However , ▁a ▁lo cks ▁was ▁constructed ▁at ▁the ▁mouth ▁of ▁the ▁river ▁in ▁ 1 8 0 7 ▁by ▁engineer ▁F . ▁W . ▁Con rad ▁( d . ▁ 1 8 0 8 ). ▁After ▁this ▁the ▁Old ▁Rh ine ▁( here ▁called ▁the ▁U it water ing sk ana al ) ▁did ▁not ▁flow ▁naturally ▁into ▁the ▁sea , ▁but ▁was ▁held ▁back ▁by ▁a ▁lock . ▁When ▁necessary , ▁the ▁lock ▁can ▁be ▁opened ▁to ▁allow ▁the ▁river ▁to ▁flow ▁out ▁to ▁sea . ▁The ▁shore ▁and ▁the ▁entrance ▁to ▁the ▁canal ▁were ▁also ▁strength ened ▁by ▁d ikes ▁ ▁During ▁World ▁War ▁II , ▁most ▁of ▁the ▁buildings ▁of ▁Kat w ijk ▁aan ▁Ze e ▁were ▁demol ished ▁by ▁the ▁Germ ans ▁to ▁make ▁way ▁for ▁the ▁Atlantic ▁Wall . ▁In ▁the ▁d unes ▁south ▁of ▁Kat w ijk , ▁many ▁b unk ers ▁from ▁World ▁War ▁II ▁can ▁still ▁be ▁found . ▁ ▁Since ▁the ▁ 2 0 th ▁century , ▁Kat w ijk ▁aan ▁Ze e ▁is ▁a ▁popular ▁se as ide ▁resort s ▁and ▁the ▁village ▁grew ▁explos ively . ▁In ▁ 1 9 8 0 – 1 9 9 0 , ▁Kat w ijk ▁aan ▁den ▁R ijn ▁and ▁Ho orn es - R ijn so ever ▁became ▁incorpor ated . ▁Rec ently , ▁in ▁ 2 0 0 6 , ▁the ▁neighbour ing