Nicholette Murray, 18, of Yonkers, was wake boarding around 5 p.m. on Lake Lillinohah in Newtown when her line became entangled with the propeller of the boat that was towing her, the agency said.
Murray, who was at the lake with family and friends, was transported to Danbury Hospital, where she was pronounced dead.
A second boating accident occurred in Windsor on the Connecticut River around 6:15 p.m.
Two people were on a tube being towed by a boat near the Wilson State boat launch when a jet ski struck them, officials said.
All three people were transported by EMS to Hartford Hospital with non-life threatening injuries.
Both incidents remain under investigation.