They came in hordes, ready for a wild time.
Several thousand rafters jammed the American River on Saturday for "Rafting Gone Wild," tugging ice chests full of drinks and, in some cases, alcohol.
Showing up in skimpy bathing suits, the rowdy crowd of youngsters was unfazed by the massive police presence and a county ban on alcohol for river activities from Hazel Avenue to Watt Avenue.
By early evening, approximately 20 arrests had been made, said Sgt. Steve Dutra of the Sacramento County Sheriff's Department.
The first arrest occurred just before 1 p.m. when a man jumped off the footbridge at Sunrise Park with a backpack full of alcohol, said R.L. Davis, Rancho Cordova's assistant police chief.
There were also four medical transports by 6 p.m., all due to alcohol, said Capt. Bryan Thomson, Sacramento Metropolitan Fire District spokesman.
Thomson said the criteria for medical evacuations were that people were "so intoxicated they can't take care of themselves. They need to be evacuated."
There were 39 medical transports last year, Thomson said.
For the most part, this year's event was much tamer, thanks to the heavy police presence. Last year, more than 3,000 people took part in the event, with 23 people arrested.
"It became so chaotic," Davis said. "It was a mass casualty scene."
Saturday evening, Thomson said, "We've had very little problems. There were some, but not compared to what we've had in the past."
He said roughly 2,000 to 3,000 people rafted from near the Sunrise Boulevard bridge to River Bend Park.
During the afternoon, it became clear that the army of rafters was gaining the upper hand, as officers, spread thin, struggled to defuse the mounting number of incidents.
Police emphasized they were trying to ensure everyone's safety.
As early as 10:30 a.m., revelers began arriving. Law enforcement made its presence felt, with officers manning checkpoints around the river, checking that no alcohol was brought in.
Authorities were trying to prevent a repeat of violence and widespread drunkenness that marred past events.
Eighty-eight officers from multiple agencies, including the Sacramento County Sheriff's Department and Sacramento County Parks Department, along with 70 firefighters, were mobilized.
"I hate to say this, but it's almost like a military operation," Sgt. Greg Johnson of the Sacramento County Sheriff's Department told the group of emergency personnel during a morning briefing at Rossmoor Park in Rancho Cordova, where a command post was established.
A steady stream of rafters quickly ramped things up after 11 a.m. Within the hour, booming music and loud yelling could be heard along the three miles between Sunrise and River Bend Park.
The alcohol ban was well-publicized in the media and online.
About 200 rafts were rented Saturday, according to Dave Hill, owner of American River Raft Rentals. He said this is a typical number for Saturdays in July and August. He said there were about 50 cancellations after the alcohol ban was announced.
Early on, most rafters denied bringing alcohol.
"We heard there was no drinking," said Melissa Chavez, 22, a restaurant server who traveled from Vallejo to attend.
But other partygoers weren't so shy about defying of the ban.
Ty Zeissler, a 22-year-old from Rancho Cordova, and his friends were carrying two coolers when they encountered a patrolling officer on a side trail.
The officer told them to take the small cooler, loaded with 12 cans of beer, back to their car.
After the officer left, Zeissler said the larger cooler, which was topped off with sodas and water bottles, also contained beer. "It's underneath the other cans," he said.
Sacramentan Nikki Janssen, 26, voiced disappointment over the ban, noting that she was a "responsible drinker."
"It would be nice to float down with a beer," she said.
In 2011, a sandbar known as Gilligan's Island was the focal point of chaos after dozens of drunken revelers gathered there. Witnesses described deputies and rangers having difficulty keeping up with the large and unruly crowd. Fights erupted on the riverbanks and rocks were thrown at rafters, they said.
This year, authorities were proactive, cordoning off the island and adjacent bank with yellow police tape. Two officers on watercraft maneuvered to prevent rafts from landing. Still, that didn't stop throngs from gathering nearby.
At 3 p.m., 100 people parked their rafts at the next bank. With music blasting, a few downed cans of beer.
Police swarmed the site to shoo away the partiers. Two helicopters circled overhead, issuing verbal orders through megaphones.
One rafter, Paul Lopez, questioned whether police had authority to force people off areas not cordoned off with police tape.
"We're just trying to have fun. Nobody is fighting," the 19-year-old said.
By day's end, rafters left the park smoothly.
"(The alcohol ban) kind of put a damper on some people's day. It was probably good," said D.J. Wilson of Sacramento, who was with a group of eight.
Call The Bee's Richard Chang, (916) 321-1018. Follow him on Twitter @RichardYChang.