RAPID CITY, S.D. (AP) — An estimated 100 cattle drowned when they fell through the ice on a reservoir that straddles the South Dakota-Nebraska border.

Mike Carlow tells the Rapid City Journal that he’s never seen anything like it in his 40 years of ranching. South Dakota Stockgrowers Association President Bob Fortune also says such incidents involving a large number of cattle are rare.

Carlow’s theory is that a windstorm pushed the cattle to seek shelter behind a tree line near the reservoir, and too many of them ventured onto the ice at the same time.

The cattle belonged to Mike Carlow and his brother, Pat Carlow. They ranch on the Pine Ridge Indian Reservation. They estimate their loss at about $300,000. Mike Carlow says the cattle were not insured.