BILLINGS, Mont. — The death of a tourist who left a boardwalk and fell into a boiling, acidic spring in Yellowstone National Park shows the challenges that rangers face as they confront soaring numbers of visitors — including some who break the rules.

No significant human remains were left to recover after Colin Nathaniel Scott, 23, of Portland, Ore., slipped on some gravel and into the treacherous water, authorities said. He was on a college graduation trip with his sister and might not have realized he was breaking park rules by leaving the pathway, said a colleague from Pacific University.

His death comes amid a spike in visitor misbehavior as the 2.2 million-acre park gets more crowded, drawing tourists never exposed to wilderness on such a large scale. Scott and his sister went off the boardwalk in a geyser basin dotted with dangerous boiling springs and where warning signs sometimes go unheeded.

‘‘This is not a resort. This is not a zoo. This is not a farm or ranch. This is a place that will kill you, and people are not used to that,’’ Yellowstone historian Lee Whittlesey said.

Six people were videotaped Wednesday by other visitors who saw them walking off the trail at the park’s Grand Prismatic Spring, Yellowstone officials said.

After Scott’s sister reported the fall, rangers navigated over the fragile crust of Norris Geyser Basin to try to recover his body. They halted the effort ‘‘due to the extreme nature and futility of it all,’’ said a park spokeswoman.

Associated Press