This was my duck coop setup a few years ago. There was / is a tiny flowing "pond" just outside it, but no run.
They used to put themselves in at night and I would then close the ramp/door.
These days they prefer to stay in the extra chicken run year-round during the night.
"River sand", "construction sand" "concrete sand", "septic sand", "beach sand", "play sand", etc, seem to be generic terms for sand that may vary considerably between suppliers and regions.
From all of my inquiries I've determined that for a coop, it's best to use sand that is "washed", but...