For a few hours on a recent Saturday, the Sammamish River came alive with a roar. Two- and four-cylinder hydroplanes, averaging 8 feet in length and weighing 400 pounds including the driver and engine, sped along the river reaching speeds approaching 60 mph.

Seventeen drivers participated in this year’s Kenmore Hydro Cup on April 13. The roster of newcomers, old-timers and famous drivers ranged in age from 9 to 72. Zooming along the river one a time, most driving while on their knees, they sped past homes and parks from the Kenmore boat launch ramp to the eastern Kenmore city limits and back, in all a 2 ½-mile course. Some participants drove runabouts that slice through the water, while others used hydroplanes, which glide over it.

First held in 1934, the Sammamish Slough races were once a big draw when boats sped from Kenmore on Lake Washington to Redmond on Lake Sammamish, over 20 miles, when the river connected the two lakes. Tens of thousands used to watch racers navigate curves and narrow passages, dodging logs and sandbars.

“It was almost a rite of passage for a racer to end up in the water,” wrote Phil Dougherty for HistoryLink.org. ”A slight miscalculation on a curve when a fraction of a second made all the difference, or hitting an obstacle in the water, could flip a boat and send the driver into the drink.”

Rick Sandstrom, from Bothell, remembers many racers failing to finish. He was one of them. Now an announcer of the event, Sandstrom said he “spun out and flooded the engine the first time” he raced in the early 1960s, though he finished it the next year.

“Back in the day when they ran all the way up to Lake Sammamish the attrition was pretty high,” he said. “I think a lot of them purposely didn’t make it because there were so many parties along the way.”

An accident that injured a spectator in 1976 ended the race for decades. As the riverfront became populated, some residents also complained about the noise.

In 2014, the race returned as an exhibition, sponsored by the Seattle Outboard Association, a local club, and under the umbrella of the American Power Boat Association.

It attracts racing families, such as the Kellys from Bonney Lake.

J. Michael Kelly is last year’s Seafair champion. He participated in the Kenmore exhibition with his kids Carson, 14, and Asher, 8, and his dad, Jeff. Kelly has run the slough exhibition three times since 2014. His grandfather and his great-uncle were racing in the early 1950s. Then his dad and uncle started in the 1980s.

“There’s a lot of history here,” he said. “I’m pretty positive that every one of my family members have gone up and down the slough at one time or another.”

For this race, he helped his dad with his old C Hydro that they used in the 1980s.

“We pulled it out of the wrappers in the garage and brushed all the dust off the motor. This is basically vintage stuff that we’re going to be running,” Kelly said. “This is what he was winning all his nationals and setting records with.”

The race also included kids. Ryan Burks helped his son Ryder, 11, in and out of the hydroplane they built through the Hydroplane and Raceboat Museum’s J-Hydro program.

“Last year was our first race season,” Burks said. “It’s all my son lives and talks about now.”

Racers will be at it again at Silver Lake in Everett on June 1 and 2.