25 years ago I used to fish the Aroostook River which flowed from Maine into New Brunswick. It more or less was dead in Maine but below the dam near the border in NB it was outstanding. Back then I used to be able to go to the border check station once a year and let them know who I was and that I would be crossing the border on the "River Road" to fish. I think there was a small concrete marker on the side of the road to mark the border.