According to the elemetary illustration on this USGS site, your concern is not
completely unfounded.


http://ga.water.usgs.gov/edu/earthgwaquifer.html

Your lake is most likely an extension of a subterranean aquifer. If the water
level in the aquifer is drawn down substantially by the municipal well, the
lake level could drop as well.

Whether or not this is likely at your particular site would depend on a long
series of geologic and hyrdologic variables.
If you're really concerned, get together with some like-minded neighbors and
hire a hydrological engineer to study your specific situation. It's likely the
municipality may have done this already, but almost as likely that the study
results could have been "interpreted" in the city's favor.