floating pontoon type thing to use as a patio on river

[CraigW]

ok, I know it sounds weird but we were going down the river near to our (hopefully) new house and some of the people who had river houses, seemed to have structures built to float on the water.

Effectively like a raft with barrels underneath with a decked area above with railings round it and seating. They were obviously using their mooring space to have an extra outdoor area.

Does anyone know what these things are called or where to get one short of making one?

[CraigW]

so i just discovered