Can Dwarves Swim, and other watery stuff...

When Gimli came out of the Caves of Aglarond, he compared it to " a grotto at the bottom of the sea", with corals, anemones, etc.

As far as I know, Gimli never even saw the sea until after he went on the Paths of the Dead. How would the landlubber Dwarf know what the sea-bottom looked like?

Can Dwarves swim? Have they been underwater?