The Newburyport municipal dock
is a fantastic location, and they even have a few moorings (they claim 4, but last time I was there I only saw a couple.)
It's first come, first serve. Come mid-week and you should be OK. Be aware that there is a day rate, and an overnight rate. Unless you come late and leave early the next day, you end up paying both for your whole stay.
Failing that, there are a number of good marinas
in the area, check Active Captain
I wouldn't count on anchoring
. The current
in the Merrimack is strong, and reverses, and there's not many places out of the channel that would work. But maybe someone local knows of a good spot I haven't found yet.