(CBS/AP) – A 9-year-old boy from Highland Park, his cousin, and his aunt were rescued from Lake Michigan on Friday, about 12 hours after they were reported missing while kayaking off Door County.

Around 4 p.m. Thursday, Thomas Alter went kayaking off Peninsula State Park with his aunt, 43-year-old Allison Alter, and her son, 9-year-old Zach Suri. They had planned to paddle to Eagle Harbor in Ephraim, Wisconsin, but never returned.

“People go out not realizing how fast conditions can change in the big water,” said Door County Sheriff’s Lt. Jeff Farley.

The rental company called 911 to report them missing when they didn’t return, and the Coast Guard launched a search-and-rescue operation.

The Coast Guard launched three response boats and three Dolphin rescue helicopters, and notified other boaters over marine radio to be on the lookout for the kayakers and report any sightings, and assist if possible.

The Door County Sheriff’s office, Sturgeon Bay Fire Department, Ephraim Fire Department, and state authorities from Wisconsin and Michigan also assisted in the search effort.

A C-130 search plane from the Royal Canadian Air Force also joined the search, and spotted the trio around dawn Friday near Whaleback Shoal, a reef in Green Bay, about 14 miles north of where they launched their kayaks.

“These kayakers were very lucky to survive this emergency situation because they did not have a way to let anyone know they were in trouble,” said Karl Willis, with the Coast Guard 9th District Command Center in Cleveland. “A personal locator beacon would have immediately alerted us to their distress and directed our rescue crews to the scene within minutes. Fortunately, the rental operator called 911 and we had the support of our Canadian partners. Without those elements, this case might have ended in tragedy.”

The Coast Guard said the three kayakers were lucky they stayed in to their boats, making it easier to spot them in the water, and preventing them from suffering a severe case of hypothermia from the frigid water.

“Any time you’re out on a boat or kayak, you always stay with the boat,” Coast Guard Petty Officer Stanley Rittner said. “As soon as you get in the water you get cold.”

A helicopter plucked them from the lake, and they were taken to a hospital to be treated for mild hypothermia.

Allison Alter had tethered her kayak to the boys’ kayak, Farley said.