FLAGSTAFF, Ariz. (AP) - A huge sense of accomplishment rushes over rafters as they conquer the last big rapid on the Colorado River through the Grand Canyon.

FLAGSTAFF, Ariz. (AP) A huge sense of accomplishment rushes over rafters as they conquer the last big rapid on the Colorado River through the Grand Canyon.

Hands fly in the air. Fists pump. Screams echo through the canyon walls.

Then someone breaks out the tequila for a celebratory drink on the aptly named Tequila Beach.

Alcohol is part of the culture of rafting in the Grand Canyon, a chance to let loose as the responsibilities of daily life are on hold during weekslong trips.

But drinking can make an already risky backcountry adventure dangerous. It has contributed to deaths and, federal investigators said this week, incidents of sexual harassment by male employees of the National Park Service on trips the agency led. The Park Service last year banned alcohol on its trips conducted for research, education or sightseeing. The move came while the Department of the Interior's Inspector General investigated an accusation that the national park's chain of command of mishandled harassment complaints.

The ban on alcohol doesn't apply to commercial companies the general public can hire to go down the 280-mile stretch of the river or private trips that are won through a lottery system.

Nighttime is prime time for drinking as rafters sit around a campfire, playing music and sharing stories, not unlike a camping trip or house party elsewhere. Most choose beer, launching their trips with hundreds of cans strapped by the case to the sides of boats and stashed in compartments. Others choose wine or hard liquor kept in bags or plastic containers because they take up less space and pack more of a punch.

A trip sans alcohol is rare.

"That's not to say everyone on every trip drinks alcohol, of course, no," said Jack Billings, of Eugene, Oregon, who prefers boxed wine on river trips. "But to say we're not going to have any? That would be unheard of."

The Park Service doesn't allow the crews from 16 companies that have river concessions contracts to drink while they're operating boats or for four hours before they get out on the river, but they can once their duties are done for the day.

Companies once brought wine and kegs of beer on trips for passengers but that stopped long ago. Guests now bring their own, though some companies have a no-alcohol policy.

The private, or self-guided, trips have the most relaxed rules. They are highly coveted non-motor trips that launch year-round, even in the sweltering heat of the summer and blistering cold of the winter. The Park Service rangers brief participants before their trips but generally make no mention of excessive drinking.

Larry Lorusso, of Clarksburg, Massachusetts, has celebrated with tequila after Lava Rapid a 20-second ride that has rafters holding tight to a rope as water thrashes around them. He's seen people belligerently drunk and been the guy accused of drinking too much.

He has accepted beer from a commercial trip looking to unload it and finished off what alcohol was left on what he thought was the last night in the canyon, he said.

"To me, it would be sacrilege to bring any alcohol out of the Grand Canyon," he said.

Both commercial and private boaters say their trips have the kind of checks and balances needed to avoid the type of abuses that federal investigators outlined on those led by the Park Service. The investigation released Tuesday found that male employees in the Grand Canyon's river district preyed on female co-workers on river trips, propositioning them for sex and retaliating against them when they refused. No one outside the Park Service was implicated in the investigation.

A Park Service official said that alcohol consumption seemed to play a part.

John Dillon, executive director of the Grand Canyon River Outfitters Association, said commercial companies risk losing their contracts if they don't abide by the Park Service regulations and have policies against sexual harassment. Guides urge passengers to drink water over beer in the arid environment, he said.

"If that's ever an issue, guides cut it off and say 'absolutely no more,'" he said.

Private trips usually include friends or family, rafters say, and a sort of community policing exists. One person is the trip leader by winning the lottery, but that doesn't necessarily make that person in charge. When strangers mix, tension can arise sometimes over alcohol.

John Hulburd lobbied a crew to reduce the 70 cases of beer, eight gallons of wine and 21 bottles of hard liquor planned for a 21-day private trip he joined last year but with little success. The split among drinkers and mostly non-drinkers soured the trip, as did the shards of glass left by broken liquor bottles in the sand and the trash created when beer cans escaped into the river, he said.

"Since there are so many opportunities for people to get hurt going down big rivers, I am sorry to see no effort made to restrict the amount of alcohol being consumed," said Hulburd, of Ridgway, Colorado. "I believe this should change, given what is going on."

Christa Sadler, a Flagstaff resident who has been a commercial guide for 30 years, has no problem with people drinking and having fun, although she doesn't have a taste for it. She's concerned that people can fall into the river at night, injure themselves on jagged rocks or become lost when drunk.

A Colorado woman who had been drinking disappeared from her campsite in early 2013. Her body was found floating in the river months later.

Commercial rafting trips can cost more than $3,000 a person, but pricing can vary based on factors including time of year and the length of the trip. The cost of private trips can vary by wider margins.

Scott Knies, of San Jose, California, has been on 10 Grand Canyon river trips over 20 years. He said he'd rather not go with people who are too drunk to care for themselves or others.

"You can't be accountable, safe and a good tribe mate if you are too buzzed," he said. "Everyone on our trips knows this and pulls their weight. This is a serious wilderness experience, not a three-week party."