Unfortunately, this place gets very crowded, so you've got to pick your times.
The best tide is usually about 2-3 hours before low tide all the way down to low slack.
This is when the herring usually show in massive numbers. Don't even try to
go weekends -- it's like urban guerrila warfare. I'd suggest weekdays very early
in the morning to midday; weekday afternoons to eves you'll have company, especially
when the keepers start showing.
I'm not all that familiar with street names, but I'll try to direct you. Go down
Land Blvd past Lotus and keep going for another mile or so until you get to
Rutherford Ave. Take a right onto Rutherford heading back towards Boston.
About a half mile down, take a left at the lights at City Square (the bridge
you see before you take the left is Charlestown bridge). Take a right immediately
after you take the left. You'll come to an intersection. C-Town Navy Yard is on the left
and the Charles River Locks are on the right. Go right. Proceed a half a mile
and you'll see the red brick locks buildings on your left. Park in the dirt lot.
At the locks, you'll see guys livelining herring from the lock "balcony" and railings.
You'll see the bridge on your left. And straight in front of you you'll see a
huge pool filled with herring and sometimes stripers. You should be able to
flyfish this bowl from the rip rap without too much difficulty. For a more productive area
walk left, walk under the Charlestown Bridge and then turn right and wade out in
front of the bridge. There are "moby" stripers hanging by the bridge abutments.
For patterns, I'd try herring imitations or clousers (for schoolies).
It's a tough place to fish because of crowds, but it's convenient and holds
some real big fish. Good luck!