Welcome aboard!
If you're looking to keep and eat fish, check this site, as a lot of the rivers are contaminated with mercury in the area:
http://db.state.ma.us/dph/fishadvisory/
You'd probably have better luck at some of the local ponds, which you have an abundance of being in Concord. Check the google maps in the area, and you'll find a lot of lakes that are a pretty good bet. I don't live that far away, so if you can't find anything, send a PM - I've fished a lot of water in the area.