MONTREAL -- The City of Montreal was expecting the first results of water-quality testing of the St. Lawrence River on Friday, three days after Montreal's sewers began diverting raw sewage away from a treatment facility and directly into the river.

Richard Fontaine, head of waste water management, said the first sets of data will come from testing for fecal bacteria in the water, while results of chemical testing take roughly 96 hours to complete.

He said the city expects the results to indicate the river is polluted.

"It's clear the tests are going to confirm there is a sewage discharge," he said. "But the most important tests are the ones we take during and after the end of the discharge, to ensure the plume doesn't have long-term negative effects."

Early Wednesday, the city began dumping eight billion litres of raw sewage into the river to access and perform critical repair work on the support arches of a major sanitary sewer as well as relocate a snow chute.

Late Friday, the city announced that 17 kilometres of the interceptor was reopened and wastewater was being treated in that sector again.

The city has said the work must be completed by late Tuesday.

Jean-Francois Blais, who works with the Universite du Quebec's research institute, said the discharge plume is probably not any more polluted than the water that is directly released from the treatment facility under normal circumstances.

"Everything that is soluble is not really removed by the treatment station," he said. "In the case of bacteria and micro-organisms, there isn't any disinfection that goes on."

He said the difference is that the treatment centre removes solid materials and phosphorus.

Blais also cautioned against reading too much into news reports that indicated the river water at some points is currently 40,000 times more polluted than normal.

"(The news reports) don't really have any value," he said. "You have to look at it from the bigger picture. Anyone would have been able to tell you that if you take a sample from contaminated water it's going to show its contaminated."

He said in a few days the normal flow of the river will dilute the discharge and water levels will return to the way they were last week.

Mayor Denis Coderre said work on the sanitary sewer is progressing.

He said on Friday 34 of 56 deteriorated support arches have already been removed.

"Working conditions are not easy (in the sewer)," Coderre said. "We will let them do their work. We said the work will be done in maximum ten days, hopefully before, but we won't be putting any undue pressure on (workers)."