The Guardian (2006)

Genre: Action | Adventure | Drama
Starring: Kevin Costner, Ashton Kutcher, Sela Ward

Plot:
A high school swim champion with a troubled past enrolls in the U.S. Coast Guard's "A" School, where legendary rescue swimmer Ben Randall teaches him some hard lessons about loss, love, and self-sacrifice.

http://www.imdb.com/title/tt0406816/
http://en.wikipedia.org/wiki/The_Guardian_(2006_film)