A seaplane with two people on board crashed Saturday morning into the waters of Clear Lake and spectators on hand for an air rally rushed to scene, pulling the two occupants to safety.

The pilot and passenger, both men, escaped with what the Lake County Sheriff’s Office said were non-life threatening injuries. Their names were not released.

A witness said one of the men appeared to have suffered a broken leg. Lake County Lt. Corey Paulich said one man was treated at the scene and the other was flown to an out of area hospital.

Paulich said the plane sank into the lake and its removal would be arranged by the county’s water resource department, the owner of the plane and his insurance company. The area where the plane sank was marked with buoys, he said.

Allen Kenitzer, a spokesman for the Federal Aviation Administration, said in an email the crash occurred under “unknown circumstances.” He said the FAA and the National Transportation Safety Board would investigate.

Paulich said the Sheriff’s Office would not comment further on the circumstances surrounding the crash.

The plane that crashed was involved in the Clear Lake Seaplane Splash In, an annual seaplane rally open to the public, with festivities based in Lakeport, according to a description on the website of the Lakeport Main Street Association.

Sebastopol resident Jessica Kilcullen said she was on a boat in the lake with a friends and family watching the seaplane activity when they noticed an unusually large splash. They saw other boats travel in that direction and followed them to investigate.

“We just saw the tip of the plane straight up and down, bobbing in the lake,” Kilcullen said.

Kilcullen said spectators from other boats retrieved the people inside the plane. One of them appeared to have a severely broken leg, she said. The other appeared to suffer several deep cuts to his face.

The seaplane event offered aerial demonstrations, music and other attractions, according to the Lakeport Main Street Association. Lake County News reported that the annual gathering started in 1979.

You can reach Staff Writer J.D. Morris at 707-521-5337 or jd.morris@pressdemocrat.com. On Twitter @thejdmorris.