Rivergate

Rivergate, the Citadel of Clan Dagonet, was built on a wide river. It cut across it like a great wall — or rather, a series of walls, descending from tall cliffs like steps meant for a giant. 

It was both a dam and a lock. The highest wall held back the powerful current. Each step below it was separated by a vast chamber with towering gates, which could be filled with or drained of water with the help of ancient enchantments.

A ship traveling to or from the Stormsea could descend from the cliffs or scale them due to the ancient system of locks, never leaving the river. At the same time, nothing could swim further upstream without destroying the Citadel — and even then, the assailant would have to crawl out of the water and travel by land with the locks destroyed.