Emergency crews are expanding their search for a 4-year-old girl who apparently fell into the Powder River east of Buffalo on Sunday evening, Johnson County Sheriff Steve Koziek said Tuesday.

By the end of Tuesday, crews will have searched a 15- to 17-mile section, he said.

About 6:30 p.m. Sunday, the Johnson County Search and Rescue, Johnson County Fire District No. 1 responded to a call at the Powder River Rest Area on Interstate 90, according to a news release from the sheriff’s office. The rest area is about 30 miles east of Buffalo.

The girl and her father were apparently walking across the icy river when they fell in. He was pulled out and taken to the Johnson County Health Care Center and treated for hypothermia.

Koziek said his office is using Natrona County's air boat, and it has brought a cadaver dog to look. Campbell, Sheridan and Waskakie counties also have offered assistance.

Changing river conditions caused problems Monday night because snow packs have melted in the Bighorn Mountains, which increased water flow and ice jams, Koziek said. The current is going down today, he said.

Koziak said the girl's father and mother were doing as well as could be expected during a tragic time. "They need a lot of prayer and a lot of support."

The family lived in the area of the Powder River Rest Area, he said.

This story will be updated.