Washouts along the banks of a fish-bearing creek in Burnaby may have seriously harmed a rare little fish that's so endangered in Canada it's found in only four streams, says biologist Mike Pearson.

The fish is the Nooksack dace, and one of those four streams — Stoney Creek on Burnaby Mountain — recently had a bank cave in at a City of Burnaby construction site, sending sand and silt into the water.

"I am seeing some serious impacts that I don't think have been fully appreciated," said Pearson, a registered professional biologist and leading authority on the small fish.

You might not be familiar with the Nooksack dace, but streamkeepers and environmentalists have been working since the 1990s to stop the freshwater fish from going extinct, even taking the federal government to court over its failure to protect it.

The sediment spill happened at a "vulnerable" time of year for the fish, said Pearson, when the dace have normally burrowed down between rocks and boulders to find a quiet spot to spend the winter.

The sand and silt would have filled those crevices, said Pearson.

"If [the fish] are lucky enough, or mobile enough to get out of there, they're essentially rendered homeless in the middle of winter," he said.

"If they're not, they could have been buried alive."

Pearson said chum salmon, which also spawn in the stream, appear to have "dodged a bullet" in the spill, because most had not yet laid eggs when it happened.

Stoney Creek mike Pearson

Biologist Mike Pearson walks along Stoney Creek in Burnaby, where he fears a recent sediment spill has damaged important habitat for the endangered Nooksack dace. (CBC)

Habitat not protected

Nooksack dace used to be plentiful in B.C. and Washington state, but is at risk because suitable habitat has been damaged or destroyed, according to Fisheries and Oceans Canada.

In Canada, they live in shallow streams in the Lower Mainland — an area with "accelating urbanization" that threatens the fish, according to the Species At Risk public registry.

Erosion of banks and other spills into creeks aren't uncommon either, said Pearson.

He isn't trying to lay blame in the recent bank collapse, but does point to the need to legally protect the "critical habitat" for the Nooksack dace, which was mapped and defined by law after environmentalists took the government to court.

That protection would require a cabinet order from the Trudeau government — something that didn't happen under Harper's Conservatives, said Pearson — or a roll-back of changes to the Fisheries Act, which weakened habitat protection.

"Even in a fairly major incident like this, our existing laws just don't cover it any more," he said.

The city of Burnaby said it was following federal guidelines during the construction work — which was repairing a culvert so a similar collapse wouldn't happen.

Mayor Derrick Corrigan said the city is committed to protecting its waterways.

With files from Kiran Dhillon