Volock dam blocks water from the Volashnic Sea from going into the Aquashnic Sea and vise-versa. Secondly the dam has two sluices, with only one open at a time it allows ships to travel between the two seas but stops contaminated water from getting into the Aquashnic Sea.
the construction of Volock dam started around the same of time of King’s Crossing but it was finished in only around 5 years because of it being significantly less complicated.