ST. JOSEPH TOWNSHIP, Wis. - A search for a missing boat on the St. Croix River ended with the discovery of three people who likely suffered carbon monoxide poisoning -- including one woman who died from the exposure.

The St. Croix County Sheriff's Office was asked to conduct a welfare check around 5:28 p.m. Sunday on a boat that was somewhere on the river, after attempts to contact the occupants were unsuccessful.

Authorities were told the group had planned to camp at a beach on Saturday but hadn't been heard from since that time.

Water patrols from Washington County found the boat about 15 minutes later, in the area of Highline Beach in St. Joseph Township, directly across from the Xcel Power Plant in Bayport, Minn.

Authorities note the beach is only accessible by boat or a private road.

During a search of the 34-foot, 1989 Wellcraft pleasure boat, three people were found. Justin Roskos, a 25-year-old Hastings man, and Hayden Johnson, a 27-year-old River Falls, Wis. man, were taken to the hospital for treatment of apparent carbon monoxide poisoning. A 24-year-old woman, identified as Ashley Speer of Glenwood City, Wis., was pronounced dead at the scene.

The boat was registered under Roskos name.

The investigation is ongoing. Authorities say additional information will be released as it becomes available.