Swimming?

[simply-juniper.livejournal.com]

Where can one go swimming around here? I have a car and am willing to travel up to 30 minutes outside the city. Usually we go to Walden Pond or Revere Beach, is there anywhere else? No pools please, I prefer natural places meant for swimming (clean lake, ocean, pond). It'd also be nice to know if there's a fee to get in.

Thanks!