Back to the Massachusetts lake, as noted in the Wiki link, the locals refer to it as Webster Lake. Although there are several alternative spellings, this one shown at a shopping plaza near the site has 45 letters, add the word "Lake" and you're up to 49 letters:
A version was even put to music. If you want to learn how to say it, learn this song (lyrics included)!http://www.youtube.com/watch?v=yhL4rg7yO4E
From a philatelic standpoint it's too bad they never had a post office, as it would have been a real challenge to get that name in the CDS on a postmark!