Over the last five years, a new generation of extreme kayakers has started plunging down increasingly large waterfalls in a bid to reach ever-greater adrenalin highs. But what do experienced kayakers attempting such a stunt need to consider?
Professional photographer Lucas Gilman took this breathtaking picture of professional US kayaker Pat Keller plummeting straight over the cliff face at La Paz Waterfall in Costa Rica at high speed. Mr Keller escaped with only a broken hand - fractured when he hit the water at the bottom of the 120ft (36.5m) fall.
For waterfalls bigger than 35ft (10.6m), the critical issues are the line of trajectory and facing the right direction in the right position.
"If a kayaker leans backs on the lip, their spinal cord will take the impact at the bottom," says Simon Westgarth, director of adventure kayaking specialists Gene17.
Instead he teaches kayakers to lean forward as they brave the rush of raging rapids. But it is a delicate balancing act - over-rotate and you are ejected into the falling froth.
POSITION IN SPOUT
In La Paz, Pat Keller rides the waterfall in the middle of its "spout" - which is about 3m wide, so he has about 1.5m of water either side of him. But experts say where a kayaker positions himself depends on individual style and every drop is different.
For the La Paz plunge, Pat Keller used a Dagger Nomad. The curvy round-bow boat is about 2.5m long, made of polyethylene plastic and buoyant enough to resurface quickly.
Although kayakers are able to manipulate the path of their body in much the same way as skiers and mountain bikers, the constantly flowing water adds another dimension. The key is to try to go with the water, rather than clear it.
"When these professionals are freefalling they want to be in the Oregon Tuck, with a curved back," says Paul Robertson, brand manager of Dagger Europe.
The paddle presents another potential liability. "It should be parallel to the kayak so that it isn't blown out of their hands - and doesn't break their nose or dislocate their shoulder on impact."
The landing is the most important - and most risky - part of extreme kayaking. Get it wrong and it could result in a broken back.
"A kayaker doesn't want to land flatly," says Mr Westgarth. "He needs to lean forward, tuck in and make his shape as efficient as possible."
Some experts advise a furious forward stroke of the paddle on plunging into the pool to get in the right position.
"The key is to follow, not fight, the flow of the water - because after falling 120ft (36.5m), a kayak can hit the plunge pool at about 50-60km/h (31-37mph)," says Mr Westgarth.
A kayaker that rides a 120ft (36.5m) waterfall into a lake will descend about five to 10ft (1.5-3m) under water on impact - and take about two or three seconds to resurface - according to Mr Robertson. But he says it depends on the volume of water cascading down the waterfall - the more water there is, the longer a kayaker will stay submerged.