Let us know how it goes. I've a friend right now that is setting up a local freshwater steam tank, and is using "live rock" substrate right from the stream. Lots of my customers have what I call "bay" tanks. See, on LI we have about four or five different ecotypes to choose from. Many South Shore residents have Great South Bay tanks, with the shallow water fish and some of the tropical exotics that get brought to us by the gulf current. These tanks are sandy bottomed and nice tanks with sea horses, butterfiles, fluke, baby shrimps and stuff. They try to grow sea grass in their tanks, but sea grass doesn't do very well once it has been uprooted, and it's not a good idea to go picking through endangered sea grass anyway.
I'm a personal fan of the "sound" tanks. The Long Island Sound has the most interesting bottom, all rocks and algae. Great beds of -Ulva lactucca- cover it. Simply take the rocks right off the bottom and instert them into the tank and you get all sorts of interesting critters. Sea stars, muscles, clams, spider crab, hermit crabs. Sand perch if you can catch them, baby flounders, pipefish and shiners nearshore, little stripers. It's really cool, and they eat right off the rock. If your rock dies off, no problem, skip it back out into the Sound and get another. I'm a big fan of the algae garden<G>.
Then we've got the estuary areas, and the freshwater lakes and streams that are crawling with small mouth bass, pickeral, sunfish, freshwater clams, trout. A freshwater tank is the one my friend wants to do since he's a stream in his backyard.
I don't know of anybody except the big name aquariums that have large offshore tanks. Some of the triggers though, them be eatin' fish! The NY Aquarium of Coney Island has a great Hudson River display with huge stripers in it. HUGE!
~~Colesea