Josh Tranby and his friends were wakeboarding on Lake Marion in Lakeville on Tuesday morning when they did a double-take: A half mile across the lake, a helicopter nose-dived about 50 feet out of the sky smack into the water.

"We saw the helicopter going from side to side, and all of a sudden, we saw it go down and he hit," said Tranby, 22, of Anoka.

The wakeboarders sped their power boat over to a shallow cove lined with homes where the chopper had crashed, said Trevor Pearson, 27, of Bloomington.

The helicopter and its pilot, Kevin Rossan, 37, from Michigan, had been dropping pesticide pellets for mosquito control when the craft developed engine trouble; he guided the chopper about an eighth of a mile and crashed into the lake about 11:30 a.m., said the Dakota County Sheriff's Office.

The pilot was out and moving slowly toward shore when the wakeboarders pulled up, Pearson said. He, Tranby and Justin Janacek, 27, of Stillwater, jumped into the frigid lake to help the pilot, who had a cut on his forehead and an injured back.

"He kept saying, 'Be careful with my back,'" Janacek said. Two women aboard were nurses and advised minimal back movement, so they didn't try to get the pilot, wearing a sweatshirt and cargo pants, onto their boat.

The pilot was barely standing in about 6 feet of water, Janacek said. "I held his shoulders and Josh brought his feet up. Trevor submerged the wakeboard under his body and he said, 'That feels better.' The three of us walked him [about 30 feet] in to shore."

Rossan was taken to Hennepin County Medical Center, where he was reported in satisfactory condition Tuesday afternoon. He works for Scott's Helicopter Services of Le Sueur, Minn., hired by the Metropolitan Mosquito Control District, said agency spokesman Mike McLean.

McLean said Rossan was an experienced pilot who intentionally landed in the lake after his engine failed. The helicopter wasn't fully loaded because Rossan had been dropping pellets before the engine stalled, he said.

McLean said county deputies, who had a water patrol boat at the scene, told him it appeared the pellet tanks were intact. He said the pellets contained methopreen, a slow-release chemical that kills mosquitoes.

"We think it will be cleaned up before there are any adverse effects," McLean said. The state Agriculture Department is investigating because of the pesticides involved, he said, and the chopper's fuel also could be an issue.

The Federal Aviation Administration and National Transportation Safety Board are investigating what caused the Bell 47 helicopter's engine to fail, the Sheriff's Office said.

The pilot crashed in a cove off the 19100 block of Orchard Trail. The water was shallow enough that the top of the chopper was visible from the yards of the homes about 40 feet away. The 560-acre lake straddles Interstate 35 between 185th and 205th Streets W.

Lakeside resident Richard Artes was on the phone in his living room when he heard "a whoosh sound." Artes said he glanced out his back window and saw the top of the chopper blades above the water. He rushed outside, as did his neighbor, and heard cries for help.

"I saw the pilot swimming this way," Artes said. "He was yelling, 'I need help. My back hurts.'"

Artes said he and his neighbor, standing on their docks, couldn't help much because they have bad backs, too. Soon the wakeboarders' boat arrived to rescue the pilot, Artes said.

He said the pilot "did a good job of missing my house."

It was a cold trip ashore, Janacek said, especially since the trio didn't have their wetsuits on.

"I was shivering a bit," he said. "It was not brutal, but we were getting cold."

Jim Adams • 952-707-9996