ponton-bridge

A pontoon bridge, also known as a floating bridge, uses floats or shallow-draft boats to support a continuous deck for pedestrian and vehicle travel. The buoyancy of the supports limits the maximum load that they can carry.

Most pontoon bridges are temporary and used in wartime and civil emergencies. There are permanent pontoon bridges in civilian use and carry highway traffic and allowing ships or boats to pass on the river or lake being crossed. Permanent floating bridges are useful for sheltered water crossings if it is not considered economically feasible to suspend a bridge from anchored piers. Such bridges can require a section that is elevated or can be raised or removed to allow waterborne traffic to pass.

Source: Wikipedia