Forty-two-year-old Doug Witmer was competing on Lake Winnebago in the High Cliff Triathlon in Sherwood, Wisconsin.
The triathlon was sponsored by the Midwest Sports Events of De Pere, Wisconsin.
Witmer lived in La Grange with his wife and two young children.
A family friend describes his as a very involved parent who had many friends.
Funeral plans have not yet been released.
As of Sunday afternoon, the death was still under investigation.