New Hampshire man vanishes during swim in Guatemalan lake Justin Booska mysteriously disappeared while swimming in a Guatemalan lake.

 -- Justin Booska is an avid swimmer. So much so, his brother said, that he used to routinely paddle in his parents' pond to rivers and lakes wherever he roamed.

That's why when Justin Booska mysteriously vanished earlier this month while attempting to swim across a crater lake in Guatemala, Benjamin Booska couldn't believe it.

"He's an athlete and a very strong swimmer," Benjamin Booska told ABC News in a phone interview from his Denver home.

Justin Booska, 27, has been missing since Jan. 6. He was with friends in Santa Rosa enjoying a beach day at Laguna de la Arza.

Booska was "hanging on the beach" on the north side of the area and took a dip to "get to the south side" where he believed a coffee plantation was, his brother said.

The waters of the lake, Benjamin said, are not known to be turbulent.

"It's not known for strong tides," Benjamin added. "It's all fresh water, no predators -- it's calm."

As Justin was "most of the way across" to the other side of the lake, Benjamin said, a boat carrying one of his friend's relatives headed out to "check on him and make sure he wasn't hungry."

And Justin, Benjamin learned later, gave no signs he was in any distress.

"He waved back that he was okay," he said.

Somewhere between 3 and 5 p.m. local time, Benjamin said Justin's friend and his family realized he was nowhere to be found.

"His friend alerted local authorities...they got a hold of my parents," he said.

A local firefighting brigade was dispatched and a search party began that night and into Sunday around the lake and the feral land around it.

The response swelled with police, soldiers in the military, drones, a helicopter and dive teams, all directed with efforts by both the Guatemalan and U.S. embassies.

Back home, Justin Booska as a child attended the prestigious Holderness boarding school before going to Brandeis University, where he graduated with a degree in women and gender studies.

The outgoing traveler stayed local for a while advocating for women who suffered from domestic violence, his brother said.

Recently, Justin shifted gears and tended bar at a local tavern in Waltham, Massachusetts, and worked as a representative to a microbrewery, his older brother said.

It also meant more time and energy to travel, even though his brother said he was frugal.

"He wanted to live life and had always been interested in South and Central America," Benjamin said.

His disappearance has drawn interest from many supporters, including New Hampshire Congresswoman Carole Shea-Porter.

“I was heartbroken to learn that Justin is missing in Guatemala," she said in a statement. "I am praying for his safe return, and I am thinking of him and his family every day. This search must continue, and I will do everything that I can to make sure that it does.”

The U.S. State Department, too, said it has been briefed on Booska's disappearance.

"When a U.S. citizen is reported missing overseas, we cooperate with search efforts by local authorities," an official said in a statement. "We stand ready to provide appropriate assistance to U.S. citizens in need."

Beyond the reach of diplomats and public servants, Guatemalan locals have also dedicated whatever they can to track down Justin.

"There was one lady and she had seven Guatemalan dollars, and that was all she had and she gave it up to help find my brother," he said.

A local newspaper, Prensa Libre, reported that volunteer firefighters had still been looking for Booska at least eight days after his disappearance.

The family has started a crowdfunding campaign to keep the effort going to recover Justin, and repay that woman and others who have made it their mission to find him.

"We want to help these Guatemalan firefighters and the community there that are dedicating themselves to finding Justin," Benjamin Booska said. "Whatever money is not used in the search will go to the local Guatemalan community... to help them get back to where they were before the search.

"And get them ready for it if this ever happens again."

And his parents are preparing to head to Guatemala to help find their youngest son and not give up on the chance that Justin is still alive.

"We hope he made it to the other side and he fell and hurt himself and couldn't extricate himself from that situation," Benjamin said. "That he couldn't help himself."