Favorite places to swim and paddle.

Though privately maintained through the Fosters Pond Association, it is open to the public. Check out the website.
 
Pomps Pond in Andover: https://www.andoverrec.com/pompspond/index
Can be reached from Shawsheen River if you put in at Dale Street, though it has to be done very soon since the access part of the pond (back side of the beach area) is full of lili pads and weeds making it hard to paddle. June 22 the pond is open for swimming with lifeguards, small fee, but easy access.
 
The sandy beach is reserved for residents but others can swim nearby.