According to the Tennessee Wildlife Resources Agency, Larry R. Stacy, 60, and Christopher R. Stacy, 32, both of Blountville, were injured in the 8:30 p.m. crash.
The elder Stacy remained hospitalized at Johnson City Medical Center Monday with serious injuries.
The accident occurred near the 422 river mile on the Watauga Arm of Boone Reservoir.
The 18-foot Bass Tracker boat the Stacys were riding in downstream collided with a boat occupied by Terry Hamm, 47, of Johnson City; Richard Ellison, 53, of Elizabethton; and Darrell W. Pierce, 44, of Johnson City.
Officials said Hamm, Ellison and Pierce were traveling upstream in a 19-foot Javelin boat when the crash occurred.
TWRA spokesman Allen Ricks said Monday that "several Good Samaritans" responded to the accident. The Stacys were taken by pontoon boat to Winged Deer Park, where they were then transported by Sullivan County EMS personnel to JCMC for treatment.
Occupants of the other boat were not injured.
TWRA wildlife officers continued to investigate the crash on Monday.
Also over the weekend, a 21-year-old woman died Saturday night from injuries she sustained after jumping into Fort Loudoun Lake and striking a boat propeller, authorities said.
Erica Nicole Watty apparently jumped from a 21-foot Regal runabout about 8 p.m. as the other boat occupants, three adults and one juvenile, prepared to return to Canal Boat Ramp on Tellico Lake, according to the TWRA.
The other occupants of the boat pulled Watty, who was not wearing a life preserver, from the water and returned to the Canal Boat Ramp. Watty was then transported to Fort Loudoun Medical Center, where she was pronounced dead.
Last year, there were 16 boating fatalities in Tennessee. In 2005, there were 10 boating fatalities in the state.
There were 107 "serious injury" accidents in 2006, resulting in 129 injuries.