Numerous wild horses managed by the Bureau of Land Management were found dead late last week and additional horses have died since the discovery, BLM officials reported Tuesday. The cause of death of 40 wild horses is under investigation.

The horses died near a water source in the extreme northwest portion of the herd management area, about 210 miles northwest of Las Vegas, which is within the U.S. Air Force Nevada Test and Training Range.

According to a separate news release from Sandia National Laboratories in Albuquerque, N.M., more than 40 horses died near the north end of the main dry lakebed at the Tonopah Test Range, which serves as a drain-off area for the dry lake.

"Due to the heat, location of the water and the low water levels," Sandia contact Stephanie Holinka said, "Tonopah Test Range representatives believe the problem might relate to water quality in that area."

The military alerted BLM late Friday that they had seen some dead horses. The area is restricted to public access and the Air Force is providing access to the BLM. Saturday, BLM went to the site and found 25 dead wild horses and an antelope.

A water pond on a dry lake bed is suspected to be the source of the problem. BLM and the military are placing a water trough and are hauling water. Water samples have been collected and a veterinarian was at the site Wednesday to assess horse health and perform a necropsy.

Samples will be sent to the California Animal Health and Food Safety Laboratory in Tulare, Calif., for analysis. Preliminary results are expected by Friday, toxicology testing will be conducted by U.C. Davis and could take up to a week.

Holinka said authorities are trying to prevent further access to the area until test results are in. Materials for barricades are being assembled in case they are needed.

About 250 wild horses use this part of the herd area and about 70 of those animals use the area near the pond. The pond has been a source of water for the herd since the early 1980s. BLM and the military are determining the best way to segregate the pond from the horses.

The BLM will provide information when test results are obtained and as other actions are taken.

These horses are in a different part of the Nevada Wild Horse Range than the area BLM conducted an emergency gather earlier in July. BLM removed 178 wild horses on the eastern edge of the range because of a lack of water. BLM has scheduled a gather to remove about 800 to 850 excess wild horses from the herd area in December to bring the herd to an appropriate management level of 300 animals. There are 1,100 to 1,150 wild horses in the herd area at this time.