A large bison blocks traffic in the Lamar Valley of Yellowstone National Park as tourists take photos of the animal. A record number of park visitors has transformed its annual summer rush into a sometimes dangerous frenzy, with selfie-taking tourists routinely breaking park rules and getting too close to animals. (Matthew Brown/AP)

Record visitor numbers at the nation’s first national park have transformed its annual summer rush into a sometimes-dangerous frenzy, with selfie-taking tourists routinely breaking park rules and getting too close to Yellowstone’s storied elk herds, grizzly bears, wolves and bison.

Law-enforcement records suggest that such problems are on the rise at the park, offering a stark illustration of the pressures facing some of the country’s most treasured lands as the National Park Service marks its 100th anniversary.

From Tennessee’s Great Smoky Mountains to the Grand Canyon of Arizona, major parks are grappling with illegal camping, vandalism, theft of resources, wildlife harassment and other visitor misbehavior, according to the records obtained through a Freedom of Information Act request.

In July alone, law-enforcement rangers handled more than 11,000 incidents at the 10 most-visited national parks.

In Yellowstone, rangers are recording more wildlife violations, more people treading on sensitive thermal areas and more camping in off-limit areas. The rule-breaking puts visitors in harm’s way and can damage resources and displace wildlife, officials said.

Often the incidents go unaddressed.

Inconsistent records, including a recent switch to a new reporting system for criminal offenses, makes it difficult to identify trends that apply uniformly across the major parks.

But the records reviewed by the Associated Press reveal the scope of visitor misbehavior is huge. In Yellowstone, administrators and outside observers say the park’s problems have become more acute. That threatens its mission to manage its lands and wildlife “unimpaired” for future generations.

Beyond incidents that lead to citations are many more that result in warnings. More than 52,000 warnings were issued in 2015, up almost 20 percent from the year before.

The top 10 parks by visitation collectively hosted almost 44 million people last year, according to National Park Service figures. That’s a 26 percent increase from a decade earlier, or more than 9.1 million new visitors combined at Great Smoky Mountains, Yellowstone, Grand Canyon, Yosemite and the other national parks on the list.

Yellowstone boasts the most large, dangerous carnivores among those parks, but each has its risks. In Rocky Mountain National Park, it’s elk that become more aggressive during mating season. In Yosemite, it’s towering waterfalls where visitors insist on swimming near the edge. In the Grand Canyon, it’s squirrels habituated to humans and sometimes quick to bite.