A weekend flash flood has severely damaged the Transcanyon Waterline, the sole pipeline supplying water to millions of annual visitors and year-round operations at Grand Canyon National Park.

Park officials estimate that roughly 40% of the 12.5-mile (20-km) pipeline may have been damaged, although a full assessment was still underway. Deputy Superintendent Brian Drapeaux said officials anticipate that miles of the pipeline could have been destroyed.

The damage comes as the National Park Service is already undertaking a more than $200 million project to replace and upgrade the aging waterline. The existing pipeline, completed in the 1970s, has experienced more than 85 breaks since 2010.

The Transcanyon Waterline conveys water through some of the canyon's most rugged terrain, moving water from the South Rim down to the Colorado River and back up toward the North Rim. Repairs can require helicopters and are complicated by steep terrain and limited access.

The latest damage has forced the park to implement significant water conservation measures on the South Rim, including shorter showers, limiting toilet flushing and turning off faucets when water is not needed. Overnight accommodations have also been halted as officials work to preserve stored water for essential operations, including emergency response, law enforcement, medical services and park facilities.

The ongoing Transcanyon Waterline project, which began in 2023 after more than a decade of planning and funding, includes replacing portions of the existing pipeline, constructing helicopter pads and water treatment facilities and relocating the water intake farther down the canyon. Engineers selected flexible steel for the replacement pipeline to improve durability while accounting for the logistical challenges of transporting materials through the canyon.

The latest flooding highlights the vulnerability of critical water infrastructure in remote areas where extreme weather can compound the challenges posed by aging infrastructure and difficult access.