Authorities said fast-acting park rangers helped avert a tragedy when they pulled a family of five from frigid waters after their boat sank Sunday at Union Reservoir.Fire officials and paramedics were called to the Longmont reservoir at 5:16 Sunday on reports that a family's boat had sunk.Within minutes, Park Rangers Ian Champa and Roy Palmeri responded in a rescue boat where the boat sank and pulled two adults and three children to safety, said Laura McConnell, spokeswoman for Mountain View Fire Protection District.The entire family was transported to Longmont United Hospital and treated for hypothermia, she said."They were very, very lucky," McConnell said in an email.It was a cold day with gusting winds, she said. "It is unclear if the boat sank due to mechanical issues or if the wind was the main factor."Fire Battalion Chief Roger Rademacher said, "The boat took on water and later sank, based on reports of witnesses."Fire officials treated nine other people for hypothermia at the reservoir on Sunday.Another boat, carrying three adults and three children, took on water and they called for help because of cold, McConnell said.The group's boat made it to shore and they had some hypothermia symptoms, she said. But they were otherwise OK.Three boys, all under age 17, were fishing from the shore or a dock when the wind kicked up, blowing cold water on them, McConnell said. The boys started having hypothermia symptoms. They were treated by paramedics and released to a parent at the reservoir."Despite the amount of warmer weather we have experienced over the past week, people need to remember that we are still in the winter months," McConnell said."People need to be aware that although ice may not be on the lakes, streams and reservoirs, the water is still in frigid temperatures," she said, warning that people without proper gear can quickly develop hypothermia.