Story highlights The mayor says there was no other option to complete needed repairs

A local environmental group says people are outraged over the dumping

(CNN) The city of Montreal is dumping 2 billion gallons of raw sewage into the St. Lawrence River over the next several days, an action the mayor says is necessary to make repairs and improvements to the city's wastewater system.

Mayor Denis Coderre said he understands that the discharge is not a popular move.

"If we had other options, we would have taken them, but we had no other option," he said at a news conference Tuesday, hours before the work began.

City officials are warning residents not to swim in or otherwise come in direct contact with the river as the operation is underway, and to avoid flushing diapers, wipes, sanitary napkins and other foreign objects down their toilets -- items they're not supposed to be flushing anyway.

The city says it's taking several precautions to make sure the river, its banks and its wildlife suffer no lasting harm.

Read More