Greater Victoria cannot continue to dump its raw sewage into the Strait of Juan de Fuca, says a scientific report commissioned by the Capital Regional District.

Every year, billions of litres of screened but untreated sewage are dumped into the ocean off Victoria.

The debate over the lack of a treatment plant in B.C.'s capital city has caused waves for decades.

Many municipal officials have argued that dumping 129 million litres of sewage into Juan de Fuca Strait every day is environmentally benign, as the fast-flowing tides naturally treat and flush the waste.

But the new $600,000 report, released Wednesday by an independent panel of scientists from across North America, says that's not sustainable.

Sewage triggering 'negative changes'

The sewage is triggering negative changes in the marine environment that will eventually lead to more serious effects, says the study by the Society of Environmental Toxicology and Chemistry.

"The reliance on dilution and natural dispersion processes in the Strait of Juan de Fuca is not a long-term answer that can be lived with," said panel chair Bill Stubblefield.

The chair of the Capital Regional District, Victoria Mayor Alan Lowe, says he's pleased with the report, as he has always supported a secondary treatment program.

"What this does is verifies what we're doing now, we cannot do in the future."

A sewage treatment system could cost as much as $500 million, with Ottawa picking up part of the tab.

Greater Victoria's municipal leaders plan to meet on the issue later this month. But they may soon have little choice in the matter, as the federal government is expected to mandate secondary-sewage treatment as a national standard.