submersible bridge

A submersible bridge is a movable bridge whose deck is lowered well below the surface of the water, allowing boat traffic to cross over the sunken deck.

The deck opens the navigation route by moving downward into the water. Boat traffic passes above the lowered deck rather than beneath a raised span.

This controlled movement distinguishes the form from a fixed low bridge that is merely flooded. The lowering must provide enough clearance over the deck for the intended boat passage.