Just to update this dormant thread. I've gone diving in a couple of lakes east of Hartford - mainly Coventry Lake and Bigelow Pond. I also talked to the Coventry police department and a local DEEP rep regarding regulations. The Coventry police could only speak for Coventry, but indicated that the rules were mainly don't do it from the launch, use a dive flag, and don't be stupid about it. Fortunately, for Coventry Lake there are quiet hours on Sunday from Noon-4pm which means you don't have to worry about jet skis and the like. There also isn't a rule about diving from a kayak, so you can launch a kayak and then dive from that no problem - although we have locations for shore entry. Also, the end of the lake with the launch is really shallow and the prevailing winds often cause unsafe swimming conditions due to e. coli on that end of the lake.
Overall situation in Coventry Lake isn't terrible if you can do a shore entry toward the middle of the lake or do it off a kayak. Visibility has varied from 10' down to about 4'. In general the lake bottom is silt over rocks. There are numerous larger rocks and because the lake is
generally an L shape that gets deepest in the middle, natural navigation is pretty easy. There's usually enough fish around to make it a little interesting - mainly sunfish, but also perch, crappies, bass, and occasionally a walleye. However, they're not really used to eating vienna sausages from the hands of divers yet. Perhaps we'll have to work on training them. There's the usual lake crud on the bottom - some beer bottles, cans, tires, and surprisingly, we've found two engine blocks that were dumped in the lake.
The biggest issue with Coventry Lake is that it gets very busy with water skiers and jet skis. Visibility tends to be best early in the morning and it has gotten progressively worse as the summer has gone on.