My family went to Eau Galle regularly when I was growing up -- if I remember right (I could hear then, I just forget), it was pronounced "Oh Gally" even though it wasn't spelled with an "i". There are a whole lot of French names in the area that are pronounced in completely Americanized ways.
I'm just curious, why would they go to Eau Galle on a regular basis? How far a trip was it for them?
I have many relatives in Eau Galle, and all of them call it as you stated, "Oh Galley." (rhymes with valley)
In all my 30+ years, the town has always been about 200 persons, I'd guess. Back in the 70s, they had three taverns, two grocery stores, a gas station, cheese factory, feed mill, and post office (but no home delivery).
These days, they have one market (Dis-n-dat), a tavern (maybe two?), and that's about it. The feed mill burned down circa 1976.
Oh, they added a generator to the dam again about ten years ago.
Just remembered--there used to be a little resort up there (prior to 1964 I think) called Welch's Point. People could rent cabins, buy groceries and beer at the little store, play on the beach, bring or rent a boat, etc.
It's now a county park, but the old people still call it "The Point."
Trivia: Caddie Woodlawn's home is a few miles from Eau Galle. Also, my Grandma told me that Laura Ingalls Wilder's (?) family had some doings around the area.