We sent our middle school son to kayaking camp for a couple of summers, which is run through the MoCo Rec department. I think it ran from 8:30-4 or so, and involved a two-night overnight trip to the Chesapeake at the end of the week. It was for middle schoolers specifically (ages 12-14 I think) and he loved it.
Our kids just returned from Camp Hidden Meadows in W. Virginia, which they love - they go for a two-week session and always come home exhilarated and exhausted. It is very well-run, ACA-accredited, and in a beautiful setting. Lots of activities, so there is something for everyone.
I have no experience with Calleva, but it gets rave reviews:
http://www.calleva.org/content/summer-camps