The State Fire Marshal’s been called in to investigate a boat explosion that happened Sunday at East Lake Okoboji marina. Department of Natural Resources investigators say they have “no definitive answers” to what caused a 33-foot-long Sea Ray “cabin cruiser” to explode while refueling. The boat’s a total loss. Four people were injured badly enough to be taken to a local hospital. A 29-year-old woman and seven-year-old boy from Rockport, Illinois, a 51-year-old man from Lake Park, and a 32-year-old man from Minneapolis, Minnesota were hurt, but authorities say their injuries were not life-threatening. Investigators say about 20-dollars worth of gas had just been poured into each of the boat’s two tanks when the explosion occured. A D-N-R news release refers to the “Handbook of Iowa Boating Laws and Responsibilities” — mentioning that a boat’s ventilation system is to run at least four minutes after fueling before the engines are started to ensure fumes trapped in the boat aren’t ignited, but, again, the D-N-R has called in the State Fire Marshal to determine the cause of the explosion. (Editors, here are the names released this afternoon by the DNR: The four people sent to Lakes Regional Health Care Center in Spirit Lake for treatment were Jenny Block, 29, and Trevor Holmes, 7, both from Rockport, Mo., Jerry Block, 51, from Lake Park, and Jason Gaines, 32, from Minneapolis, Minn. Gains was released Sunday night. Holmes was released Monday morning. The injuries were not life threatening. Others involved but who were not injured were Chris Block, 50, from Lake Park, Jeremy Block, 32, Eugene, Ore., and Molly Gaines, 31, from Minneapolis, Minn.)