The National Park Service said an unidentified man pushed the calf up the river as it was separated from its herd
Yellowstone National Park says it has killed a newborn bison in the US state of Wyoming after a visitor intentionally touched the animal.
The visitor was trying to help the calf rejoin its herd after it got separated from its mother, according to the park.
The herd rejected the calf despite repeated attempts by park rangers to reunite the young bison.
Yellowstone is now investigating the incident.
The calf had to be killed because it was abandoned by the herd and was approaching cars and people on the roadway, "causing a hazardous situation", the park said on Tuesday.
"An unidentified white male in his 40-50s, wearing a blue shirt and black pants" approached the newborn bison on Saturday after the calf had been separated from its herd while trying to cross the Lamar River.
"As the calf struggled, the man pushed the calf up from the river and onto the roadway," the park said. The newborn animal was later seen on the road around vehicles and visitors.
Interference by people can cause a herd to reject its offspring.
"Approaching wild animals can drastically affect their well-being and, in this case, their survival," the news release said, noting that people are required to stay at least 25 yards (23m) away from all wildlife, and 100 yards away from bears and wolves.
"The safety of these animals, as well as human safety, depends on everyone using good judgment and following these simple rules."