Hi,
You can try for cats in the "duckpond" area of the Charles just off of Rt.30 Auburndale. There is also a Charles river canoe rental location off of Rt. 30.
I did read a write up of this area where it was reported that the catfish like popcorn because the people who feed the waterfowl in this area feed them popcorn.
Please keep in mind that fishing for catfish is usually Bait, Bobber and sinker fishing. Which can be slow if you are "calling" the fish to your hook with stink baits and such. If you water reading skills are good then you can make your presentation to where the fish lie, which will greatly speed up your chances of hooking a fish.
Here is a link from basspro on catfishing basics:
http://www.basspro.com/webapp/wcs/stores/servlet/CFPage?storeId=10151&catalogId=10001&langId=-1&&mode=article&objectID=29703&cat=Fishing&subcatID=15&objectType=article