Went to Key West last Summer, and went on a catamaran eco-tour. saw dolphins, and kayaked around mangroves, and went to great snorkelling site. we saw barracudas and lobsters, and millions of fish. all quite near to the surface. we have 4 children then aged 12,,11,10,& 8. and they all loved it.
the crew were brilliant, one was a biologist and told us all about the ecosystem and how the mangroves were formed etc
Unfortunately I can't remember the name of the company but it was based behind the hilton near to the cruise ship docking area, and it had a female captain.