There a both private and public camping sites in the Machias Bay area.
As with all states, don't bring firewood from out of state which could carry parasites. Same is true with trailered boats.
Google listing of private campgrounds in the Machias Bay area.
Machias River - Typically used for Canoe trips.
Machias River. Has outhouse with 1 lean-to and 6 primitive camping sites. First come, first serve. Great place for fly fishing.
With facilities, first come first serve public campsites at boat launch
Machias River - MPRL
Public sites for canoe trips or taking the family out to enjoy camping. Facilities available.