Montana Fish, Wildlife & Parks has a goal of establishing five new wild sheep herds by 2022. But it's struggling to maintain the herds it has in the face of disease carried by domestic sheep.

In recent years, a number of wild herds have suffered major die-offs over the course of a single year, as sheep succumb to pneumonia. Those that survive may have a certain level of immunity, but their lambs often die, possibly infected by their own parents. As a result, the herd slowly dwindles.

How useless a death then, when a healthy lamb is killed by a careless driver. That's happened repeatedly in the Rock Creek Canyon east of Missoula, where some homeowners and an increasing number of anglers and visitors - many from out of state - escape to the woods and the river.

It's a challenge for a wildlife agency that can do little more than put up caution signs.