There's some decent diving in the lake. Some wrecks and some fish. Lots of boat traffic in the summer. There's a couple of dive shops in the area, including Morin's, Capitalland Scuba, Diving Discovery, and Adirondack Scuba. Morin's is the closest (Glen's Falls ~ 30 min from the lake) and Adirondack Scuba is the most reasonably priced (Ballston Spa ~ 45 min away from the lake). I think Diving Discovery does charters on the Lake, and I know Capitalland does, Adirondack Scuba goes up there on any given weekend (they're a small, out-of-the-garage shop) for fun dives or classes, and I'm not real up on Morin's dive schedule.
If you want any info on the area, PM me, and I'll see what I can do for you.
Lake's a bit cold right now to do any diving, still slushy in some areas. That and it's not much warmer topside. Killed our try out the new drysuit seals dive for this weekend.