Westslope Cutthroat Trout populations continue to decline in Alberta and some environmental groups are sounding the alarm over an incident in Silvester Creek, west of Calgary.

The groups say mud from a road used to haul logs was swept into critical Westslope Cutthroat Trout habitat earlier this month.

Silvester Creek runs through the McLean Creek Public Land Use Zone and is home to one of just 13 genetically pure populations of the native trout.

Logging companies and trail users are required to use only specially designated crossing points that should be designed to limit runoff into the creek.

Part of Silvester Creek has been designated as critical habitat for Westslope Cutthroat Trout and the species is listed as threatened under Alberta’s Wildlife Act.

Excessive mud can smother the eggs of the threatened fish, which will soon start spawning.

The Canadian Parks and Wilderness Society says the latest incident highlights a problem with the way the province protects threatened species.

"More broadly, we'd really like to see a forestry policy reevaluated so that this is prevented, it's not just caught and repaired. Fragile species like cutthroat trout can't handle events like this and they should be prevented in their entirety," said Becky Best-Bertwistle, from CPAWS.

Dave Klepacki is a passionate fisherman and when he saw the water he was concerned.

“The silt will clog up the oxygenation of those eggs and those eggs are at risk of dying of course,” said Klepacki. “I was surprised at how silty it was that far downstream from the actual problem with the bridge where the silt was running off of the road.”

Klepacki set out to find the source of the silt and says he came across a bridge along a logging road that had given way, dumping loads of dirt into the creek system.

“As soon as we got above those bridges upstream, water was crystal clear,” he said.

A representative from Spray Lakes Sawmills says the company is aware and took action as soon as the weather improved to stop mud and dirt from getting washed into the creek system.

The company adds that they believe that there was no environmental impact from the event.

In 2005, there were an estimated 330 adult cutthroat trout in the creek system and that number fell to just 81 fish by 2016.

The province and Fisheries and Oceans Canada are looking into the incident.

(With files from Bill Macfarlane)