2017 Red Bull Heavy Water: athletes battled 15-foot waves breaking at Ocean Beach | Photo: Red Bull

Danish stand-up paddleboarder Casper Steinfath, 23, has been crowned the 2017 Red Bull Heavy Water champion, in San Francisco, California.

Hailed as the most intense stand-up paddleboarding event in the world, the Red Bull Heavy Water put 32 of the world's best SUP athletes to an extreme paddling and surfing test.

Competitors surfed over 15-foot high waves at Ocean Beach and then had to paddle their boards across a 7.5 mile (12 kilometers) open course via Seal Rock, Mile Rock, and then past the Golden Gate Bridge near Fort Point.

The conditions were really tough. The massive northwest swell made the surf zone extremely difficult to overcome, transforming the first stage of the contest in an authentic washing machine.

Some of them struggled to get past the brutal waves that continuously kept breaking out-the-back, and forcing riders to navigate through the relentless whitewater.

Casper Steinfath: the winner of the 2017 Red Bull Heavy Water | Photo: Red Bull

The action was constantly monitored by the Maverick's Water Safety Team, and US Coast Guard, who made sure no one got lost in the heavy surf.

"Wow, did this really happen? I feel beyond stoked. Never have I felt so happy to win a race but mostly just be alive!" expressed Casper Steinfath, a multiple ISA SUP champion.

"Congrats to all that survived it. I will honestly admit I was scared shitless out there! "It was the craziest and scariest SUP race of my life!"

2017 Red Bull Heavy Water | Top 5

1. Casper Steinfath (DEN), 1h15m01s
2. Ryan Funk (USA), 1h16m01s
3. Travis Grant (AUS), 1h18m38s
4. Kody Kerbox (HAW), 1h24m16s
5. Michael Booth (AUS), 1h27m47s