Coming of age movie about a teenage boy spying on neighbor swimming nude in farm pond.

Just a guess...

The Man in the Moon (1991)
From Wikipedia:
In the summer of 1957, Dani Trant (Reese Witherspoon) is a 14-year-old girl in Louisiana... Dani and her older sister, Maureen (Emily Warfield), who is going off to college in the fall, are very close. Maureen helps take care of their younger sister, Missy, while their mother, Abigail (Tess Harper), is pregnant. Dani prefers to run off to the neighbors' pond to go swimming in the nude. It is here that she meets her new neighbor, 17-year-old Court Foster (Jason London).

https://en.wikipedia.org/wiki/The_Man_in_the_Moon