Quicksand Fans

I've had a heck of a time finding good deep mud in MA. There's tidal muck in places, but you have to be super careful that you don't get stuck, and there are often people about. Some rivers have deep mud, but it's usually only knee-deep and not very difficult to extricate yourself from. I'm wondering if anybody knows good spots in New England where there's proper river quicksand of some sort.

Long time lurker here, but I've finally made an account!