Waterford — Connecticut Environmental Conservation Police are investigating after a boat explosion sent three girls to the hospital with burns Monday afternoon.

According to Cyndy Chanaca, a spokeswoman for the state Department of Energy and Environmental Protection, EnCon police responded to Niantic Bay Boat Valet at 8 River St. about 4 p.m.

Upon arrival, officers learned a 1983 Seabird boat with an inboard motor was being fueled up at the gas dock when the explosion occurred.

Chanaca said the three girls, ages 12, 13 and 14, were onboard with a 73-year-old man, who is the grandfather of one of the girls. All four are from Bristol.

Crews took the three girls to Lawrence + Memorial Hospital, where they were treated for burns.

EnCon police and the Waterford fire marshal are investigating the incident.