RE: neponsett river fishery
I believe there is a pretty significant smelt fishery in the river below the first dam in Dorchester Lower Mills (Baker Chocolate Bldg area). No fish passage so all anadromous fishes (blueback herring most likely) are blocked at the dam.
I've caught stripers trolling clousers and deceivers in the spring from the gas tank down to the second highway bridge.
Hope that this helps.