AUSTIN (KXAN) — The coolers roll down the dock with 30-packs and hard seltzers stuffed inside.

The arms pulling them almost always belong to someone in their 20s and 30s, visiting from a faraway corner of the country, dressed in a new summer bikini or muscle tank top.

They come here by the hundreds, even thousands, on weekends. As soon as it becomes warm enough to float on a boat comfortably, bachelor and bachelorette parties show up for a reservation booked months ago to have a party boat captain take them around Lake Travis.

“I would say (it’s) 85-90% bachelor and bachelorette parties from out of state,” said Lone Star Party Boat Owner Beau Sisul. “That’s our main customer.”

Sisul has extensive boating experience, and for the last five years he’s built up a fleet of five boats that he and his team of captains charter for people looking to party.

The boats fit up to 22 people, have state-of-the-art sound systems, an upper deck and waterslides that never go unused.

Safety first

Once on board, often with a drink already in hand, these visitors are given a safety speech.

Much like a flight attendant prior to takeoff, the captain goes over all the rules. No one upstairs when the boat is moving, no drugs allowed and no jumping over the railings.

This talk runs the risk of going over the same way a flight attendant’s message often does — acknowledged, but not necessarily absorbed, Sisul said.

“You got to be authoritative without being a jerk,” Sisul said. “‘These are my rules. If you don’t buy in, we’re heading back to the dock, no refunds.’ And that sets a tone of like, ‘alright, everyone, if you see someone out of line, tell them to get in line.'”

Heading out to party, but a risk of tragedy

Often as early as 10 a.m., the party boats leave the docks by the dozens and make the short trip to an area on the water known as Devil’s Cove.

Once there, the captains will drop anchor in the small, protected portion of the lake and pass out a long rope to the other captains to tie up in rows of 10 or so boats. On busy weekends, the rows go on and on.

“I’d say easily on a holiday weekend, 200 boats in there,” said Texas Game Warden Justin Barnes, whose job includes the responsibility of responding to emergency calls in the cove.

Those calls come, and at times include panicked people on the other end of the line.

Seven people have died in the cove since 2010, the year the Travis County Sheriff’s Department started keeping detailed statistics.

“We frequently have people tell us, you know, ‘we were all swimming together, and then after 10 or 15 minutes, we just all of a sudden noticed we hadn’t seen this guy in a while,'” said TCSO Senior Public Information Officer Kristen Dark. “They know the proximity they were in, but they don’t know what happened to that person.”

While a 22-passenger boat is about as big as it gets in Devil’s Cove, boats that are in some cases more than six times bigger head to nearby Starnes Island.

The biggest of these so-called “party barges” reports being able to hold up to 140 passengers and are often used for events like fraternity and sorority parties.

These barges have also seen tragedy with the same number of deaths, seven, being reported on them as were reported in Devil’s Cove since 2010.

“Tragedy on party barges runs the gamut of situations,” Dark said. “Sometimes we’ve had people who went down the slide and never resurfaced, people who’ve jumped off the boat, people who’ve been swimming near the boat, some have fallen off the boat. Sometimes these incidents have happened when the boat was in motion and other times when the boat was stationary.”

One of those victims includes Rachel Scott, 25, who fell off the top deck of a party barge and reportedly hit her head before falling in the water. It took search teams nearly five months to recover her body.

Many of the boats have floating foam rafts known as lily pads that people will hold on to while swimming and drinking in the water.

“On a hot sunny day, alcohol is going to affect you faster, you’re going to become impaired and dehydrated faster,” Dark said. “Dehydration is something that’s going to make it harder for you to swim.”

While all boats are required to have a lifejacket on board for every guest, hardly any adults in Devil’s Cove or at Starnes Island wear them.

Sisul said his boats are either custom-made or retrofitted to add taller wrap-around railings to try and keep everyone inside the boat who’s supposed to be. He also said he trains his captains to act as a sort of “babysitter” who puts safety first.

“You can see someone thinking about doing something stupid,” he said. “You got to keep an eye on people the whole time.”

“The Wake: Secrets of Lake Travis” premieres Monday, May 29th on KXAN.com. You can watch it on KXAN at 4:30pm and The CW Austin at 7:00am and 9:30pm.