Here's my new favorite beach not 30 minutes up Route 8 in Watertown, just north of Waterbury. Forget the jellyfish at the shore, this beach comes with lifeguards as well as hiking trails in lovely Litchfield County. Just $5 will get you in. The Mattabassett Blue Dot Trail goes up to the top of a small peak overlooking the lake where, after finding a letterbox, we picnicked. It's called Black Rock due to some graphite that was mined here once, and after lunch we hiked down the red trail, which looks like the old haul road for the mine. A few geocaches later we strolled back along the lakeside trail and finally returned to the beach for a swim, which was clean and uncrowded.
There are no concessions, but the gas station (Citgo?) just down the road has a deli where we picked up fried chicken and a salad.
Later, while my daughter fished, I explored the shoreline with the old point-and-shoot. We discovered some huge snails I had never seen before and suspected they were invasives - there were so many. Sure enough, they turn out to be "Chinese Mystery Snails", which have been reported in Western Connecticut and the Hudson River Valley. The snails are native to Asia, where they are eaten, and they are also used in fresh water aquariums because they close up when water quality becomes toxic, thereby alerting the aquarium owner before the fish die.
Here are some photos of the park.