This is where they stock the broodstock salmon in Mass (2010-2011).
http://www.mass.gov/dfwele/dfw/fisheries/anadromous/broodstock_salmon_stocking.htm
Then there's also the Merrimack River too where the Salmon run free... well until they hit the dams
where they sometimes get carted off in trucks and dropped off in NH so they can continue their upriver run. But you can always try to catch them before they hit the Essex dam in Lawrence (although be sure to check your mawildlife mag that came with your license or check their website because there are some regulations about fishing for salmon near that dam).