Seven mules and two horses owned by the National Park Service (NPS) Sequoia and Kings Canyon National Parks have died after a watering system failure at a remote winter pasture in the Pixley National Wildlife Refuge left the animals without an adequate water supply, according to a June 8 statement from the NPS. The cause of the watering system malfunction is under investigation.

The winter pasture is located approximately 35 miles south of Tulare and 45 miles north of Bakersfield in California’s San Joaquin Valley. Two additional animals–a horse and a mule–have been under a veterinarian’s care since the incident. Published reports indicate six additional horses residing in the pasture appear healthy.

"This is a tragic loss for us," Sequoia and Kings Canyon National Parks Superintendent Karen Taylor-Goodrich said in a statement. "These animals were part of our team and a vital part of park operations. We are heartbroken about what happened and will be investigating this incident thoroughly."