EDMONTON -- One-time supporters of the Alberta government's plan to protect a much-loved corner of southwestern Alberta are having second thoughts about the proposed Castle provincial park.

While the New Democrat government won wide praise for the promise to protect the region's mountains, foothills and prairie, many environmentalists are now concerned the area could turn into park in name only.

"The protection outlined in early September is more symbolic than substantive," said Ian Urquhart of the Alberta Wilderness Association in a letter to Environment Minister Shannon Phillips.

On Sept. 4, Phillips announced the government would turn more than 1,000 square kilometres into a provincial park and provincial wildland area.

But the association -- along with other groups such as the Castle-Crown Wilderness Coalition -- has since written to Phillips expressing concern the government plans to allow activities usually forbidden in provincial parks such as off-highway vehicle use, hunting and livestock grazing.

"Not even (former Conservative environment minister) Ty Lund made decisions allowing hunting in provincial parks or OHVs in provincial parks," said Urquhart in an email.

All those activities have long been practised in the area. Together with resource extraction, they're among the reasons environmentalists have called for the Castle's protection.

Coalition spokesman Gordon Petersen said allowing those activities in a park would be a bad precedent.

"We don't want to win the battle for the park but lose the war because of a watered-down park designation," he said.

In his 23-page letter, Urquhart points out the existing off-highway vehicle trail network is already double what science suggests is compatible with grizzly bear and cutthroat trout. Hunting has no place in a provincial park, he writes.

Livestock grazing, he writes, tramples plants, introduces invasive species and fills valleys with manure, reducing their recreational value.

The concerns are a sharp about-face for environmentalists.

When the announcement was made, they pointed out the plan was almost twice the size as that proposed under the previous government. It also included valleys and wetlands that were previously excluded.

The government's plan still has "good bones," said Petersen. He hopes the controversial uses will be removed in its final version.

"I don't think it's set in stone, but it's certainly concerning."

The Castle area is unique in its geography and biodiversity. Mountains spring precipitously straight up from the prairie. Snow-fed streams form the headwaters of major rivers such as the Oldman.

More than 200 threatened species -- from grizzlies and wolverines to bull and cutthroat trout to rare trees -- call the Castle home.

A spokesman for the Alberta government was not immediately available.

The park proposal is currently open for public comment. The comment period closes Monday.