Greg Lords jumped off High Bridge on I-21 on Saturday, falling 150 feet - the equivalent of a 15-story building - before landing in Lucky Peak Reservoir.
Each second in the air, he picked up speed. He may have hit the reservoir at close to 80 mph - too fast for the water to safely cushion his fall. The Boise State University basketball player did not survive.Lords, 21, and a brother were boating with their family when they decided, against an uncle's advice, to jump off the bridge. Lords jumped - his brother did not.
No autopsy will be performed, but several physicians said he likely suffered serious injuries on impact.
"It's like landing on the ground," said Dr. Thomas Haga, an emergency physician who works at St. Alphonsus and St. Luke's regional medical centers.
"The water can't move away from your body fast enough to cushion you at all. Basically, you stop short.
"Things break and get torn loose inside," he said. The nature of the injuries depends on whether jumpers land feet first, on their head, or on their back or chest.
Injuries could include a broken neck, dislocated arms or legs, torn heart muscle, collapsed lungs and concussion.
Depending on how deep the water is, victims also can get hurt bouncing off rocks in the water. Whether that happened to Lords is uncertain. Water under the bridge was about 35 feet deep.
Lords likely drowned after being knocked unconscious on impact, said Dr. Gary Holland, also an emergency-room physician in Boise.
Neither Haga nor Holland treated Lords, who was pronounced dead at St. Luke's Regional Medical Center in Boise.
Police earlier thought Lords fell 180 feet, but he jumped from a girder under the bridge, not from the roadway.
No autopsy will be performed because the body had no serious external injuries, and because the accident had witnesses, said Doug Tucker, deputy Ada County coroner.
Last year in the Boise area, 24 water-related accidents were reported. Three were fatal.