What's up, man,
If you want to fish the Charles, there's a boat ramp right on Woerd Ave. in Waltham (right off Crescent St). From there, head South for the good spots (left if you're on the ramp facing the river).
I'm not sure if there's access to cochichuate (or however the F you spell it), but there's a lake right across the street also run by the state with free access (head east on rt30 for about a quarter mile, and its on the left), and if you wait til 4 or 5 in the afternoon, even the state parks you usually have to pay for are free. just keep your eye on the time. If it has a gate, it probably closes at 8, and you'll have to call the police to unlock it for you (yes, you do indeed hear the voice of experience)
hope this helps