A preliminary investigation into a deadly boat sinking early Sunday on Lake Vermilion in northeastern Minnesota found several factors that may have contributed to the incident, the St. Louis County Sheriff's Office said Monday.

In the most serious of at least three state boating disasters over the Memorial Day weekend, Casey Thomas Gilbertson, 29, of Virginia, Minn., died in the lake when the boat in which he and six other people were traveling from Bayview Resort to Fortune Bay suddenly began to take on water and sank about 3 a.m. Sunday. Two people were able to swim to Forest Lane Resort, and four others were rescued by the resort owner and brought safely to shore.

An intensive search was then launched for Gilbertson, who was found in the lake and declared dead at the scene.

On Monday, sheriff's Sgt. Nate Skelton said the boat, which authorities recovered, may have been over capacity and did not have enough life vests for the passengers it carried. "Alcohol use may also have been a factor," Skelton said in a news release.

In another boating mishap, two people were injured Sunday evening when their 16-foot fishing boat collided with a houseboat on Birch Lake in northern Lake County, the Sheriff's Office reported Monday. One of the injured was airlifted to a Duluth hospital, while the other was treated and released. Names and medical conditions were not available. No one on the houseboat was hurt. The accident happened about 6:30 p.m. Sunday, Sheriff Carey Johnson said in a news release.

In yet another weekend boating incident, three people were rescued just after midnight Sunday after a boat began to sink on a lake in northern Washington County. According to the Sheriff's Office, a woman called 911 to say she could hear people on Big Marine Lake yelling for help. The lake sits between Forest Lake and the Wisconsin border.

A member of the Scandia rescue unit and his wife, who live on the lake, launched their personal boat and found the three adults, who had swum to the west side of the bay, and took them to a boat landing, where authorities were waiting for them.

Deputies interviewed the boat driver and arrested him on suspicion of boating while intoxicated. The 23-year-old Fridley man was being held in the Washington County jail. His two passengers were examined by medical personnel at the scene and released.

Washington County deputies found the boat and are investigating.