A St. Croix County woman died from an apparent carbon monoxide poisoning Sunday after she and two others were found on a boat over the weekend on the St. Croix River.

The St. Croix County Sheriff’s Office identified the woman as 24-year-old Ashley G. Speer of Glenwood City. Two others on the boat, 25-year-old Justin M. Roskos of Hastings and 27-year-old River Falls resident Hayden L. Johnson, were found alive. They were transported to Hennepin County Medical Center in Minneapolis.

A Hennepin County Medical Center spokeswoman said Roskos was in critical condition Monday. Johnson was in satisfactory condition, she said.

“It appears to be a tragic incident that took the life of one young adult,” St. Croix County Sheriff’s Office Chief Deputy Scott Knudson said.

Deputies were requested to do a welfare check at 5:28 p.m. after the boat they were on, a 34-foot 1989 Wellcraft, didn’t show up to a beach camp where they were expected.

The boat was found about 15 minutes later at Highline Beach in the town of St. Joseph after St. Croix and Washington county water patrol officers searched the river. Only one of the boat’s three occupants was conscious when officers arrived, Knudson said.

Speer was pronounced dead on the scene by the St. Croix County Medical Examiner’s Office.

Knudson said it wasn’t clear where that spot, owned by the St. Croix Beach Club, is relative to the beach camp where the boat was expected.

He said the symptoms the boat passengers experienced led to the carbon monoxide poisoning suspicion, but said that’s not yet been confirmed.

Investigators are checking into “what may have played into the carbon monoxide ventilation issue” under suspicion, Knudson said. All indications so far were that the incident was accidental, he said.

He said the passengers’ relationship wasn’t immediately clear. The likely carbon monoxide-related death was the first of its kind in recent memory on the St. Croix River, Knudson said.