I live in Brookline and fish the Boston section of the Charles all the time with good success. There are a bunch of posts out here on where to fish the Charles. Hope this helps.
You should try Millenium Park off VFW Parkway in West Roxbury. There is also Nahaton Park off of Kendrick Street in Needham but there is a kayak rental place there and parking gets really tough unless you arrive early.
current reports are lots of algae bloom up and down the Charles. I've seen it and it reeks. The advice is to not get it on your hands and to keep children and pregnant women far away from the stuff.
and as I said, the Charles reeks just now in the heat.
i went across from Newton Canoe and Kayak last Sunday and it was awful,you couldnt cast without lines full of clumps of smelly shiz thats floating down the river!gonna try Medfield today,seems to have more current there usually and lastnites rain hopefully washed some of that crap away