Environmental groups fighting a mining company's proposal to build a winter road and airstrip along the Wind River are asking the Yukon government to block the company's bid, arguing that environmental assessors made serious errors in their review.

The Yukon Conservation Society and the Canadian Parks and Wilderness Society are opposed to the proposal by Cash Minerals to build the 178-kilometre winter road and airstrip in the area, located near Mayo.

Last month, the Yukon Environmental and Socio-Economic Assessment Board (YESAB) recommended that the government approve the Vancouver-based company's application.

But environmental groups worried that such work could lead to full-scale development in the area, and possibly threaten the Wind River watershed, have written a six-page letter to the Yukon's Department of Energy, Mines and Resources.

"What we're suggesting is that the Yukon government should realize that there are such serious mistakes in the YESAB evaluation that, indeed, the project should not go ahead," said Karen Baltgailis, executive director of the Yukon Conservation Society.

Cash Minerals, a Vancouver-based junior exploration company, wants to build the road and airstrip in order to haul fuel, supplies and equipment to uranium exploration sites it has in the area.

In giving its approval, YESAB assessors attached 46 conditions related to environmental and socio-economic concerns, including the risk of disturbing permafrost along the proposed route.

The board said the company should only bulldoze or plow the road when the ground is frozen, and then only with blades up off the ground to leave sufficient snow cover.

However, the groups said the assessment board did not raise similar concerns regarding the proposed airstrip. They also claimed the board missed key information, not even knowing how long the airstrip would be. Such information would have determined how big a scar the airstrip would leave on the land, they argued.

Baltgailis also raised concerns with the nearby Bear River, saying Cash Minerals is proposing to build the winter road on the ice for 23 kilometres — something she claimed goes against the federal Fisheries Act.

"That looks like it would actually be illegal for the Yukon government to allow this company to do this," she said.

Baltgailis said her group is studying its legal options, should the territorial government approve Cash Minerals' application without addressing the concerns she raised.