Environment Canada will conduct its own investigation into a massive discharge of raw sewage into the Ottawa River in 2006 that is already being probed by Ontario's Ministry of the Environment and the City of Ottawa.

Meanwhile, an Ottawa-area MPP is calling for a public inquiry into the sewage spill, which has been blamed for fouling an Ottawa beach.

The federal department's enforcement branch launched the investigation earlier this week under the Fisheries Act, confirmed Garry Keller, spokesman for Environment Minister John Baird, who is also the MP for Ottawa West-Nepean.

"As environment minister, John Baird is very concerned about this incident and obviously wants to ensure that something like this doesn't happen in the future," he said. "We take this matter very seriously, and we'll certainly use all the authorities available to the federal government to get to the bottom of what exactly happened here."

The sewage discharge is being investigated as a "deleterious substance" harmful to aquatic organisms.

Knowledge of the 1.2-billion litre spill became public last week. The spill has been blamed for bacterial contamination that shut Petrie Island beach for 45 days in 2006. It is believed to have been caused by a faulty valve in the sewage system that was stuck open for two weeks after a storm.

The environment ministry has said charges could be laid against the city as a result of its investigation.

However, Norm Sterling, the Conservative MPP for Carleton-Mississippi Mills said he believes government investigations won't go far enough and is calling on Premier Dalton McGuinty to launch a public inquiry.

"I think it's important for us to know not only where there should be charges against different responsible parties but if in fact there's a problem with the system."

Sterling questioned why the environment ministry waited so long to investigate the incident even though it knew about the spill several months before the provincial election in October.

Initially, the city believed that the spill had been reported to Ontario's Environment Ministry immediately as required.

A City of Ottawa worker was fired Wednesday after the city determined that was not the case and the worker had lied about when the spill had been reported.