A kelp forest was an underwater habitat that could be found on Earth. They were characterized by the presence of Kelp.
In 1986, the Cetacean Institute in Sausalito hosted a kelp forest exhibit. It was open between 11:15 a.m. and 4 p.m. (Star Trek IV: The Voyage Home)
The exhibit was neither mentioned nor seen, but details about it were on a blackboard above the aquarium lobby.