The death of a 7-year-old girl on Lake Minnetonka earlier this week was the result of carbon monoxide poisoning, the Hennepin County medical examiner has confirmed.

Sophia Baechler, a second-grader at Edina’s Concord Elementary School, died Sunday after first responders were called to a dock on Wayzata Bay and found her unresponsive. The family said she died on the family’s boat from carbon monoxide poisoning. The medical examiner ruled the death an accident.

It’s unclear what exactly caused the poisoning or if others were affected. The Hennepin County Sheriff’s Office is investigating.

Carbon monoxide poisoning fatalities from a boat have happened twice in the last eight years in Minnesota, according to state data. The toxic, odorless gas can build up from an idling motor, a generator or from a faulty motor exhaust system. Many newer boats have carbon monoxide detectors, but they aren’t required.

Sophia, who would have turned 8 in December, is survived by her parents, Benjamin and Courtney Baechler, and 5-year-old brother, Will.

A memorial fund set up for Camp Kici Yapi and Concord Elementary has already raised $20,000. The funeral, which will be open to the public, will be at 11 a.m. Friday at Our Lady of Grace Catholic Church in Edina.