Echo Lake is the best lake. You can swim from Ike's Point. Sight across the lake to Camp Beech Cliff (worked there or 7 years!), or go left to the Ledges and Echo Lake Beach.
Long Pond is another good one, as is Somes Pond.
You CANNOT swim in Eagle Lake, Jordan Pond, or Bubble Pond. Don't break the rules here. They are public water supply.
Ocean - Somes Sound on a Sunday (no lobster boats will be out); Sand Beach
Boston is not "from the area" ;-)
maybe she's born with it, maybe it's chlorine
If you're injured and need some sympathy, PM me and I'm very happy to write back.
disclaimer: PhD not MD