Day trip from Boston to a freshwater river/lake

[Beanboy]

Greetings.

Not traveling this July 4th, but was thinking about a day trip somewhere with both boats to relax with the GF and let her try out the surfski as well as test out carrying both boats. Waldon is about 30 minutes from me, but was wondering if I were some other freshwater options within two hours or so of Boston proper.

One area was Tully Lake Recreation Area, which I've been to for a triathlon. Clear lake combined with some hiking trails:
http://www.northquabbinwoods.org/entries/168

Any other recommendations?