Long Island Sound averages 60 ft in depth, with the greatest depth of over 300 ft at the eastern end. Tidal effects are strongest at the narrow western end, where all the inrushing water flow piles up and makes tidal variations of up to 7 ft. Strong tidal currents are also prevalent, and visibility tends to be poorer than the open ocean, especially at depth.
Now, most people would look at the heading on the page and think that I was crazy for diving near a nuclear power plant. Just to calm your fears, this power plant was never brought online, so there is no chance of getting radiated at this location (barring a nuclear war while you're diving). With that said, Shoreham can be a very interesting dive. Located on the north shore of Long Island (I don't know the name of the town, look on a map), it is a shallow dive with an average depth of around 16 ft. Visibility tends to be anywhere from 3 to 10 ft.