A federal judge Wednesday temporarily blocked further work on a new border fence and barrier through the San Pedro Riparian National Conservation Area.

U.S. District Court Judge Ellen Huvelle accepted the arguments by Defenders of Wildlife and the Sierra Club that construction, which already has started, needs to be halted immediately. She concluded the organizations showed there was strong evidence of irreparable environmental damage if the project is completed as planned.

The judge also noted the assessment of environmental effects of the project prepared by the Bureau of Land Management took just three weeks in August, with no opportunity for public comment; construction started less than a month later. She questioned whether federal agencies were deliberately rushing the process and the construction to get it done before anyone had a chance to object.

But Huvelle's ruling does not mean the fence - or something like it - never will be built.

Instead, it simply buys some time for the two groups to prepare legal arguments that federal agencies did not follow environmental laws in designing the nearly two-mile stretch that goes through the conservation area. The judge ultimately still could give the go-ahead to complete the work.

Brian Segee, an attorney for Defenders of Wildlife, said Wednesday's decision is still a victory. He said Huvelle's decision to issue the temporary restraining order recognizes "the irreparable harm that the border wall construction would cause."

But Russ Knocke, spokesman for the U.S. Department of Homeland Security, said his agency is convinced "that this one mile plus area along the Arizona border will not be adversely impacted by fence construction." Knocke said an appeal is being considered.

"Arizonans, and quite frankly Americans everywhere, have been clear that they want more border security," he said. "Today's ruling will not diminish our resolve to deliver it." Central to the legal fight is the decision by the U.S. Bureau of Land Management, which manages the conservation area, to conduct only an informal "environmental assessment" of the effect of the fence design on the area.

That assessment, which took just three weeks and had no opportunity for public input, proposes an impenetrable fence through much of the conservation area. It also concluded there would be no harm to the environment if a vehicle barrier built from old railroad ties were used instead of a fence in the 1,500 feet of the San Pedro River floodway as well as washes leading into it.

It is that plan which the Department of Homeland Security started constructing about two weeks ago, just a month after the assessment was completed. Segee, however, said federal law requires a full-blown "environmental impact statement" for all "major federal actions significantly affecting the quality of the human environment."

He said such a study would show that what Homeland Security is constructing will cause additional sedimentation and erosion, wiping out plants and, in turn, affecting the birds and animals who live in and around the conservation area. Gregory Page, an assistant U.S. attorney who handles environmental cases for the government, said an assessment is legally sufficient.

But Segee said the judge noted that the government already has agreed to prepare an impact statement for a similar project in Texas.