As mentioned above, most of the fresh water around here has been polluted with mercury by the coal fired power plants out west and unlined landfills. Not all of them though. The trouble is finding out which ones are clean.
http://www.mass.gov/dep/toxics/stypes/envnment.pdf
http://www.mass.gov/Eeohhs2/docs/dph/environmental/exposure/statewide_fish_advisory_poster.pdf
http://www.mass.gov/dph/fishadvisories
http://www.mass.gov/Eeohhs2/docs/dph/environmental/exposure/fish_consumption_advisory_list.pdf
The safe thing to do is only eat non-stocked freshwater fish once in a great while if at all. The stocked fish, like rainbow trout can be eaten as much as you want, or at least as often as you can catch them.
From looking at some of those sites/documents it would appear that Rainbow, brown, brook and tiger trout would be safe to eat anywhere that is stocked and lake trout and salmon are safe in Quabin and Wachusett reservoirs?
All other
people should not eat smallmouth bass, largemouth bass, or lake trout greater than 24 inches long; may eat unlimited amounts of salmon and lake trout less than 24
inches long; and should limit consumption of all other Quabbin and Wachusett Reservoir fish species to one five-ounce meal per week.
I assume all over fish species doesn't apply to stocked fish?