Pine County, MN (NNCNOW.com) - Two snowmobile accidents in Pine County this weekend left one victim seriously injured and the other still missing. Authorities are searching for a snowmobiler that broke through ice on the St. Croix River Saturday. According to the Pine County Sheriff's Office, a group of three people were traveling along the frozen river after dark, when the victim hit a large patch of open water. Witnesses say the victim disappeared in the water, where authorities believe they may have been swept downstream under the ice by river current. Authorities say the accident happened around 6:41 p.m. approximately four miles north of the Soderbeck River Landing. Also in Pine County, a victim was thrown from their snowmobile after authorities believe they struck a partially submerged island. The Pine County Sheriff's Office says the accident happened around 9:15 p.m. on Pokegama Lake Saturday. The victim was found with life threatening injuries. They were transported to a hospital in Mora. Written for the web by Jennifer Austin.