The flow of sour gas through a ruptured pipeline in southern Alberta was turned off Thursday, but a small amount of the deadly sour gas was still seeping into flood waters submerging the line.
Pipeline owner Legacy Oil and Gas of Calgary was deciding whether it was safe to send in divers to fix the break.
"There is still a bit of a trickle," said Cara Tobin of the Alberta Energy Regulator.
"The break point is quite difficult to get at. The company is looking at getting some divers in."
Ms. Tobin said the leak near Turner Valley wasn't endangering public health.
The sour gas contained one per cent potentially deadly hydrogen sulphide.
"There have not been any dangerous levels of H2S detected at any point," she said. "That has been confirmed by the company and the fire department."
The leak occurred at a section of pipe struck by debris in the rushing Sheep River, the company said in a release.
About 150 people were forced to leave their homes in the town of about 2,500 as a precaution. The evacuation order remained in place late Thursday afternoon, largely because of flooding.
The leaking section of pipe remained under water.
"If it's dangerous conditions to have divers go in the water, it won't happen," Ms. Tobin said. "If they can do it safely, they will do it as soon as they can."
An Alberta Emergency Alert earlier in the day called the rupture potentially life-threatening and urged people to move indoors and prepare for a possible evacuation.
Sour gas is a colourless, natural gas that smells like rotten eggs. It contains hydrogen sulphide and is extremely toxic, even in small amounts.
The Canadian Association of Petroleum Producers says about 30 per cent of natural gas in Western Canada is sour and some crude oil produced in the region is also sour.