By FELICIA FONSECA, Associated Press

FLAGSTAFF, Ariz. (AP) — Deep inside the Grand Canyon, on river trips that stretch for weeks, National Park Service workers have preyed on their female colleagues, demanding sex and retaliating against women who refused, a federal investigation found.

The Department of the Interior's Inspector General's report Tuesday was prompted by a complaint in 2014 accusing the Grand Canyon National Park's chain of command of mishandling complaints that trip leaders pressured female co-workers for sex, touched them inappropriately, made lewd comments and retaliated when rejected.

Thirteen current and former Grand Canyon employees filed the 2014 complaint alleging a pattern of abuse that continued for 15 years. The Inspector General's Office interviewed 80 people, 19 of whom said they experienced similar bad behavior; a park service human resources official described a "laissez faire" culture of "what happens on the river stays on the river" that continued even after the women formally complained.

Eight women said the men reacted in a hostile manner during the trips when rejected. Several accused a boatman of arbitrarily taking them to the wrong sites so that they couldn't do their assigned work. One accused the supervisor of leaving cans of human waste outside her tent. Another said non-compliant female colleagues were denied food.

The report charts a dozen instances in which park employees have been disciplined for sexual misconduct since 2003, ranging from a written reprimand to suspension and termination, but it concludes that responses to harassment complaints and any resulting discipline have been so inconsistent that many women decided against reporting them at all.

Until recently, National Park Service managers allowed river rafters to bring alcohol on the Grand Canyon trips — a policy that changed last year, as the report was being prepared.

A spokesman outlined a series of reforms under consideration, saying the agency has zero tolerance for sexual harassment.

"No NPS employee should ever experience the kind of behavior outlined in the report, and it is even more disappointing because previous efforts to change the culture at the river district of the Grand Canyon failed to improve working conditions," James Doyle wrote in an email Tuesday. Changes include requiring nightly check-in calls by satellite telephone, including a supervisor on every trip and establishing a regional ombudsman outside the park's chain of command to handle complaints — a first for the National Park Service.

One of the women who joined the 2014 complaint said excessive alcohol use is the biggest contributing factor to sexual violence on river trips. She called the other proposed changes trivial. The woman, who worked as a ranger in the river district from 2009 to 2012, said the Park Service's acknowledgement of the problem is a first step toward positive change.

"It was a culture of victim-blaming perpetuated by all levels of management," she wrote in an email. "I repeatedly sat in meetings in which victims who had reported sexual violence were degraded and discredited."

Grand Canyon National Park manages 280 miles of the Colorado River, providing emergency and medical services as well as guiding researchers, politicians and students on a dozen river trips per year. Co-workers spend lengthy stretches together, camping on the river banks deep within the towering walls. A satellite phone typically is available for emergencies only.

The report does not name any of the people involved, and The Associated Press does not identify victims of sexual harassment without their consent. It focuses solely on National Park Service trips; Commercial and private, or self-guided, river trips are conducted through different systems.

The Office of Inspector General said it had not conducted any similar investigations at other national parks.

The report focuses on allegations lodged against four NPS employees, identified as Boatman 1, 2 and 3 and Supervisor 1. Boatman 2 resigned in June 2006 after serving a 30-day suspension for taking a photograph under an employee's dress. Boatman 1 resigned in July 2013 after a 2-week suspension for groping and propositioning an employee. Supervisor 1, who served a 10-day suspension a decade earlier for grabbing the crotch of a contract employee, retired in May 2015.

Boatman 3, who was known as a "womanizer" who propositioned employees for sex, is still employed by the Park Service but is restricted from participating on river trips, Doyle said. He acknowledged having consensual sex with women in the canyon, but told investigators he approached women only when he sensed a "mutual attraction." One river district employee said Boatman 2, Boatman 3, and Supervisor 1 all tried to "get laid as much as possible" during river trips and that there was "some sort of wager . . . or challenge between the three of them . . . to see who would get laid the most," investigators reported.

A woman and her supervisor claimed they were retaliated against after their complaints led to disciplinary action against Supervisor 1 and Boatmen 1 and 2. They were given two-week suspensions and their contracts weren't renewed after Boatman 3 accused the woman of harassing him by "twerking" in his presence at a river trip dance party.

Other employees selected by senior park managers to be interviewed, denied seeing any sexual misconduct on the river. One longtime friend of Supervisor 1 and Boatman 3 described them as "free spirits" who loved to "joke around," and blamed the women for being "scantily" clothed, drinking too much and flirting with the men.

The Park Service's Intermountain Region director Sue Masica, Grand Canyon Superintendent Dave Uberuaga and his deputy, Diane Chalfant, told investigators they were well aware of the history of alleged sexual harassment on the river, if not all of these details, and had tried to change the culture. Last year, they prohibited alcohol use at any time during Park Service trips through the canyon.