Like most ideas, Rob Casey’s stand-up paddling business grew out of necessity.

Last year, he noticed wave-seekers struggling to balance on boards in Shilshole Bay without instructors. Casey, who has taught kayaking for eight years, was concerned about their safety.

“You can learn on YouTube," Casey said. "But, that’s kind of hard to do. That led me into wanting to teach.”

Casey launched Salmon Bay Paddle a few months ago. For $50, Casey teaches the basics of stand-up paddling, sea kayaking or surf kayaking for two hours. He also offers lessons for intermediates and custom guided tours.

“You can not only catch waves easier and ride longer waves, but when a wave ends, you can still paddle and get a little more out of the wave,” Casey said.

Stand-up paddling, the United States’ fastest-growing sport, is a step up from kayaking—almost literally. Paddlers mount a long board—up to 12 feet in length—stand up and comb the water with a paddle.

“It’s a full-body exercise,” Casey said.

The majority of people manage to stand up their first day on the water, he said.

The sport has roots in Venice, Peru and parts of Asia, but surfaced in modern culture in 1960s Waikiki. Surfers introduced it to the mainland in the 1990s, and it has surged in popularity in recent years. R.E.I. sells up to 10 boards a week in the summer.

Casey also has a book due next spring, the first on stand-up paddling, published by Seattle-based Mountaineers Books. It covers stand-up paddling on rivers, surf, racing, expeditions and fitness, profiling some of the sport’s pros.

Having sat down kayaking for years, Casey thought he’d seen it all.

“Standing up, you see so much more,” he said. “You see schools of fish. You see a seal coming up directly underneath you. It’s a completely different perspective.”