Antelope Island—42 square miles of prime habitat in Utah for free-ranging bison, mule deer, bighorn sheep, antelope and other wildlife—was once one of the largest islands in the Great Salt Lake. Yet, historic low lake levels have changed the landscape, turning the island into a peninsula and creating a bridge between the island and the mainland. This change in landscape spells trouble, especially with regard to disease, which “wiped out nearly all of the island’s 150 wild sheep” last year, forcing the Utah Division of Wildlife Resources (UDWR) “to kill the 26 survivors to ensure the disease would not spread,” the Salt Lake Tribune reports.

While disease could have infiltrated the island a variety of ways, officials believe it happened when a ram left the island and came into contact with domestic sheep or goats before returning to its wild herd. Yet, because the pathway to the mainland is easy for sheep to travel, park officials have decided to install an 8’ fence to, hopefully, keep the animals contained to their current habitat.

Park manager Jeremy Shaw says it will cost $300,000 to $500,000 to install the 10 miles of fencing around the island’s south end and “be built into the lakebed about a quarter mile off the island’s historic shoreline.” Once the fence is up, UDWR plans to relocate 35 bighorn sheep to reestablish the obliterated herd.

“There has been some struggle with our bighorn sheep populations recently because of respiratory disease,” said UDWR biologist Jace Taylor, who oversees the bighorn sheep and mountain goat program. “Part of our objective is to expand bighorn sheep populations where possible and to maintain the overall population in a sustainable and healthy way across Utah to provide quality opportunities for wildlife viewing and hunting.”