GRANTS PASS, Ore. (AP) — An outbreak of botulism has killed thousands of ducks at Tule Lake National Wildlife Refuge in Northern California.

U.S. Fish and Wildlife Service spokesman Matt Baun said Friday the outbreak is not unusual, but has been exacerbated by the drought.

He adds that the refuges along the Oregon-California border have not gotten any irrigation water since November.

In non-drought years the refuges get water after it has run through farms on a nearby federal irrigation project, but there has been none to spare this year. An agreement that would give more water to the refuges has been stuck in Congress.

Wildlife biologist John Beckstrand says they have picked up 5,000 dead ducks to limit the spread of the disease, and there are probably 5,000 more they couldn't find.