> When it froze in winter, people from both sides would literally come out onto the ice and it wasn't too far to get across.

That definitely sounds like the northern end of Snow Pond. It gets wider further down, but up at the top it's narrow enough that you could easily snowshoe across it in the winter.

Waterville doesn't actually have any lakes or ponds--not within the city proper, at any rate--but based on your description it sounds like either Snow Pond or McGrath Pond in Oakland could be candidates. They both have sections that are narrow so you'd easily be able to see the neighbors the way you describe, and there are numerous private roads on both. It would also be an easy drive to Colby from either one of them.

Are there any other details you remember?