A government study warns that off-highway vehicles threaten the environment in a large park planned for Alberta's southern Rocky Mountain foothills.

The study, which draws on 150 published papers, comes as the NDP government decides what activities will be allowed in Castle Wildland Provincial Park and Castle Provincial Park.

It says the region has at least 1,700 kilometres of unofficial trails and 1,600 stream crossings.

The region already has at least twice as many trails per square kilometre as other provincial and national parks in Alberta.

The report, released late last month, says there's strong evidence linking such trails to erosion, stream degradation and grizzly bear deaths.

A member of an off-highway vehicle group says the report was written to justify banning the activity in the park.

The final plan for the parks, which will cover more than 1,000 square kilometres, is expected in the spring.