(Reuters) - Yellowstone National Park rangers on Wednesday were attempting to recover the body of a man who was believed killed after falling into a hot spring at the tourist attraction in Wyoming, a park spokesman said.

Colin Nathaniel Scott, 23, was seen by his sister on Tuesday slipping and plunging into the hot spring near Pork Chop Geyser in the Norris Geyser Basin after straying some 225 yards from a wooden boardwalk designed to prevent such accidents, according to park spokesman Morgan Warthin.

“We extend our sympathy to the Scott family,” Dan Wenk, the park's superintendent, said in a written statement. “This tragic event must remind all of us to follow the regulations and stay on boardwalks when visiting Yellowstone’s geyser basins.”

The National Park Service warns on Yellowstone's official website that hot springs, where water temperatures average 143 degrees Fahrenheit, have injured or killed more people than any other natural feature.

Warthin said that on June 6 a father and son suffered burns in the Upper Geyser Basin after walking off the designated trail in the thermal area.

Last month, Yellowstone managers warned visitors to leave wildlife alone after two tourists put a newborn bison calf in their car, touching off a string of events that ultimately led to the animal's death.

Each year some four million people visit Yellowstone, the first national park established in the United States.

(Reporting by Dan Whitcomb; Editing by Alistair Bell, Bernard Orr)