The bodies of four people missing after a boat crash on the Mississippi River in Iowa were found Sunday within 100 yards of the crash site, according to the Iowa Department of Natural Resources. None was wearing a life vest.

DNR officer Paul Kay said three men and a woman, all believed to be in their 20s, were killed. Their names have not been released, pending notification of their families.

Along with the four killed, eight people were injured when two johnboats _ flat-bottomed boats often made of aluminum _ crashed in the O'Connell Slough area of the river, where the water is 10 to 12 feet deep, before 2 a.m. Saturday. One of the boats was carrying 11 people; the other had a single passenger.

Authorities scoured the river near Burlington for signs of the missing boaters Saturday before calling off the search after dark. Efforts resumed early Sunday morning.

DNR spokesman Kevin Baskins said eight people were pulled from the water soon after the crash. At least one person suffered serious injuries and was flown to an Iowa City hospital, he said. The others were taken to a Burlington hospital. Some had since been released, Baskins said Sunday, although he didn't have an exact count.

Baskins said authorities are still sorting out the cause of the crash. No charges had been filed as of Sunday.

"That's going to take a while," he said of the investigation.

Burlington is in southeast Iowa on the Illinois border, about 200 miles north of St. Louis on the river.