A couple and their 9-year-old son aboard a Cessna were shaken but not hurt after making an emergency landing in Lake Washington this morning off of Seattle's Magnuson Park.

Around 9:45 a.m., the plane that originated from Oregon and was scheduled to land at Boeing Field landed about 100 yards off shore and sank after hitting the water, said Helen Fitzpatrick, a Seattle Fire Department spokeswoman.

Someone aboard a pleasure boat nearby managed to pluck a man, woman and boy from the water and take them to safety before a fire department rescue team could arrive, she said.

FAA spokesman Mike Fergus said the Cessna 185 reported engine trouble just before 10 a.m.

Fitzpatrick said the plane sank.

"I saw the plane coming at the building and it was getting lower and lower," said Nick Parker, 17, a student intern at the National Oceanic and Atmospheric Administration, located on the shores of Lake Washington. "I was thinking 'Oh my God, it's going to crash.'."

The plane appeared to take a sharp left turn and stall in midair before rapidly descending, he said.

Other witnesses saw a wheel catch the water and the plane cartwheel into the lake nose first, said Seattle police spokeswoman Debra Brown. A speedboat with four passengers quickly came to the rescue. The plane sank within minutes.

"The people on the plane were very, very shaken," Brown said. "

Brown said the passengers were a 41-year-old man, his 42- year-old wife and their son, all from Bend, Oregon.