The water rights behind the proposed Lake Powell pipeline are not actually coming from the project’s namesake lake, but rather from the major reservoir upstream on the Green River.

Now, Utah water officials’ new request to overhaul those rights has handed opponents a fresh opportunity to thwart the proposed pipeline just as federal officials are about to release a long-awaited environmental review of the $1.2 billion project, which would funnel 82,000 acre-feet of water from Lake Powell to St. George.

The request, known as a change application, seeks to shift the the water rights’ “point of diversion” from Flaming Gorge Reservoir to a spot 400 miles downstream behind Glen Canyon Dam. The change, which also keys into where and how the water would be used, is needed to fit the goals of the pipeline, which is to bolster water supplies for Utah’s mushrooming Washington County.

The application was filed now because the timing made sense at this stage in the project’s development and has no bearing on whether the pipeline gets built, according to Joel Williams, assistant director of the Utah Division of Water Resources.

Environmental groups hope to block or at least delay the project’s approval if they can persuade Utah State Engineer Teresa Wilhelmsen to deny the change application filed April 13. Exhibit A in the many protests filed is the Colorado River system’s chronically diminishing flows in the face of climate change, long-term drought and overallocation.

“This change application is predicated on this idea that there’s plenty of water available for Utah in the Colorado River in the future,” says Zach Frankel, executive director of the Utah Rivers Council. “We don’t think there’s going be enough water for Utah’s share of the Colorado today.”

In a related development, the federal Bureau of Reclamation expects to release a draft environmental impact statement Friday that will identify a “preferred” alternative for the pipeline, which would move water 140 miles through southern Utah and northern Arizona.

A 1922 interstate compact divvies up water flowing in the Colorado River and its many tributaries among seven basin states and Mexico. For decades, Utah has underutilized its share, pegged at 23% of the Upper Basin’s flows above 7.5 million acre-feet, while the three Lower Basin states have historically drawn water in excess of their allocations, largely to fuel urban growth and corporate agriculture.

The Lake Powell pipeline, authorized by the Utah Legislature in 2006, can be seen as the state’s effort to put more of its share to use by sending it to rapidly growing Washington County. Kane County pulled out in April after concluding it wouldn’t need to supplement its existing water sources for decades. Yet the new change application includes that county, which had planned to reap 4,000 acre-feet.

That indicates the Kane County Water Conservancy District hopes to keep the door open to tapping water flowing through the pipeline in the future.

The pipeline’s diversion would use less than 6% of Utah’s 1.4 million-acre-foot allocation of the Colorado, according to the state’s change application.

“There are no vested Utah water rights that will impacted by the the project,” the application states. “Approval of the application will provide economic benefit to the citizens of Utah and water security, drought protection, and long-term reliability for the citizens of southern Utah.”

This water is critical to sustaining the “existing economy of the area and meeting future demand,” it adds, and represents a “wise use” of Utah’s allocation.

Environmental groups dispute that assertion.

“The proposed transfer would send scarce water to an area that profligately wastes it,” the Center for Biological Diversity writes in its protest. “Rudimentary water conservation measures could supply the purported water needs of [the St. George] area. Thus, sending water to this area to fuel more growth is by definition wasteful.”

Utah holds rights dating back to 1958 to water in the tributaries of the Green River but has yet to develop them. To fill the pipeline, the state promised a total of 86,000 acre-feet of these rights to the Kane County and Washington County water districts many years ago.

“Under the proposed change application, the water right will still be used for the construction of a public water supply project,” Williams says. “The application seeks to change the place of use from the area served by the Central Utah Project to the fast-growing southern Utah region.”

The language in the application proposes changing the place and nature of use from agriculture in the Uinta Basin to municipal uses in Kane and Washington counties.