RIVERTON, Wyo. (AP) — Authorities believe a 33-year-old man drowned after he ended up in an irrigation ditch in Riverton.

A woman told investigators she saw the Lander man standing near the edge of the water before she went back inside her home Tuesday evening. After she heard some kind of commotion, she went outside and the man was no longer there.

His body was found about a mile and a half downstream Tuesday night.

The victim's name has not been released, and Fremont County Coroner Mark Stratmoen says an autopsy is planned for Thursday.

The water in the drainage ditch began to rise mid-afternoon Tuesday and washed over two culverts and a private bridge in the area a short time later.