Sarah Morris of BC Emergency Health Services said first responders received the call at 2:15 p.m. on July 15.
Morris said three ground and one air ambulance crew have been rushed to the scene.
Paramedics are with the patient and are co-ordinating a means to get the person to the hospital.
Squamish Search and Rescue and Squamish Fire Rescue were also at the scene.
Squamish SAR rescue manager B.J. Chute said the incident occurred around the rope swing area on the west side of the lake.
There were two swimmers in distress, and their friends pulled them to shore, he said.
Paramedics and fire crews hiked in, and a SAR boat arrived to shuttle everyone back to an ambulance.
Rescuers also had a helicopter on standby at the airport, in case any further help was required.
***Updated 5:13 p.m. with details from Squamish Search and Rescue.
