The massive enlargement of the Gross Dam in Colorado is back on.

A federal judge has pulled back her previous injunction, stating in her decision, "Petitioners have not shown that they would be irreparably harmed if the Gross Dam construction were to be completed." 

It means the completion of the dam is back on, after objections to a prior move by the judge filed by Denver Water, which operates the reservoir and sought the expansion in a process that dates back to 2002. Denver Water has said it needs additional capacity in its northern water system as it faces concerns about climate change and fires that could contaminate supplies.

In a ruling out late Thursday, Federal District Court Judge Christine Arguello stated, "A permanent injunction prohibiting further construction of the Gross Dam is not merited due to safety concerns."

The petitioners have been a consortium of environmental groups and neighbors of the project in southern Boulder County who filed a lawsuit in 2018 against Denver Water and the Army Corps of Engineers which approved the project, as well as the U.S. Fish and Wildlife Service. Their primary objections were to drawing water from the headwaters of the Colorado River on other side of the Continental Divide through the Moffat Water Tunnel, clearing the trees as part of the project to enlarge the reservoir, and effects on wildlife, including elk habitat.

Arguello put the completion of the dam, which will be raised by 131 feet to accommodate enlarging capacity of the reservoir by nearly threefold, on hold back in April, then allowed some work to continue.

In October Arguello had found the Army Corps of Engineers violated The National Environmental Policy Act as well as the Clean Water Act when it approved permits for the reservoir expansion. And she backed many of the opponents claims.

The water to fill the expanded reservoir capacity would be moved from the headwaters of the Colorado River on the opposite side of the Continental Divide via the Moffat Tunnel. Denver Water has maintained that will only draw during periods when the tributaries are flowing well.

In Thursday's ruling, Arguello found another kind of potential environmental injury -- in stoppage of the project.

"There is a risk of environmental injury and loss of human life if dam construction is halted for another two years while Denver Water redesigns the structure of the dam and gets that re-design approved," she wrote. 

In a statement, Denver Water wrote that it looks forward to finishing the project it called critical.

"This added storage is of enormous importance to the 1.5 million people we serve, as well to our West Slope partners who support the environmental benefits to streams and fish habitat associated with the expansion. Denver Water will continue to work through the appellate court to resolve remaining issues and ensure this long-awaited project reaches completion."

Those remaining issues also came out in the judge's order Thursday. It's not clear sailing yet for the reservoir expansion. The judge said the Army Corps of Engineers has to re-write environmental permits before the expanded reservoir can be filled to its new capacity.