A 41-year-old Crow woman has been missing for six days, according to the Bureau of Indian Affairs.

Crystal Williamson's mother told investigators that she last saw her daughter when she left with three friends to go swimming in the Little Bighorn River on June 30.

Law enforcement authorities used a helicopter to search for Williamson over the weekend, said Elizabeth Hull, as-sistant special agent with the Bureau of Indian Affairs.

Williamson's mother filed a missing person report for her daughter on July 2. Crystal Williamson is 5 feet 6 inches tall and 160 pounds, with hazel eyes and light brown, shoulder-length hair.