The Mystic Lakes are a treat any time of year.
The west side of the lakes is nearly all walkable.
A view of the lake from the path.
A mural at the Mystic Lakes Dam illustrates the Mystic River Watershed.
The paths can be close to the roadway, so it's always wise to keep alert here.
A big information board tells about the history of the river herring in the lakes and Mystic River.
The Mystic Link Trail runs along a narrow bit of land along both lakes, and this is the Mystic Lakes State Park. The other side of both lakes is mostly private land so you can’t walk all the way around the lakes, but there is lots of good walking on the eastern side. These two lakes offer lots of good walking with lovely water views.
More Resources:

All Trails for the Mystic Lakes
Recommended trails and map

Commonweatlh Page
All the rules and regs for the lakes