One person is missing and another is in hospital after what search and rescue crews are calling the "most serious rescue of the summer" in Shuswap Lake.

The incident occurred shortly after 8 p.m. Sunday, according to Fred Banham of Royal Marine Search and Rescue. RCMP and BC Ambulance were called to assist with a boat crash in Shuswap Lake roughly 16 kilometres north of the community of Canoe, B.C.

Banham said there were two boats involved in the crash, one with a white hull and one with a blue hull. Both vessels were heading towards Sicamous, when the white boat veered into the path of the blue one, he said.

Two occupants of the white boat were thrown into the water, according to Banham, and two occupants of the blue boat jumped in to help them.

Search and Rescue crews sent two boats to the scene of the crash. A 25-year-old woman who was thrown from the white boat was rescued and taken to hospital with head and back injuries. Salmon Arm RCMP said Monday that her injuries were "serious."

The other occupant of the white boat, a 33-year-old man named Ryan Hartmann, was not found. Police and SAR crews searched until 2 a.m., but were unable to locate him. RCMP say he is "presumed drowned."

The occupants of the blue boat were not injured in the collision, Banham said.

The area of the lake where the incident occurred is between 250 and 350 feet deep, police said.

The vessels involved are in police custody as investigators work to determine the cause of the collision.