While most Grand Canyon visitors are drawn to its dramatic beauty, a growing number of amateur athletes see it as a grueling challenge: a steep, sweaty 24-mile trek from one side of the canyon rim to the other.

So many are attempting the "rim to rim" hike or run, that the National Park Service announced Wednesday that it will now require permits for groups making the trip starting Sept. 15.

Park officials said the permits, which will be required for some groups of between two and 30 people, will let the park keep better track of who is on the trails, and manage stretched resources to respond to water and medical needs.

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Kirby-Lynn Shedlowski, a spokeswoman for the National Park Service, said the trips have increased in recent years.

In one busy May weekend, officials saw 400 to 600 people completing rim-to-rim trips, she said.

The service received "pretty much constant" emergency service calls for issues including dehydration and blisters that weekend, she said. Unprepared and injured trekkers triggered more search-and-rescue operations, park rangers said.

The increased influx also means more trash on the trails and overcrowding at restrooms, Ms. Shedlowski said.

Endurance sports, such as trail running and ultramarathons, have been rising in popularity and "I think this has risen…as a bucket list challenge for a lot of people," she said. "We want to ensure they have a safe experience."

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