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A 1.7-kilometre sewage pipeline has become a new home and nursery for fish and plant species in an area that once was a virtual void.

Three years after it was installed on the grainy, vacant ocean floor just off southern Vancouver Island near Sooke, a fused plastic pipe cloaked by cement ballast is drawing previously absent fish like the threatened lingcod and a variety of seaweed and sea creatures.

"That's one of the delightful aspects, because there used to be nothing there," said Tami Wetmore, an environmental engineer for Epcor, the utility company that oversaw construction of Sooke's sewer system and the marine outfall.

When the sewage system was approved five years ago to stop failing septic systems from polluting Sooke's harbour and basin, critics raised concerns that the outfall would harm marine life.

But a true sea change has occurred.

"Most people don't associate outfalls with increased life, but this pipeline structure is adding complexity to what was a flat, sandy habitat," said Jason Clarke, an engineer and marine biologist with consulting firm WorleyParsons. "It's been a rapid diversification that I haven't seen to quite this degree."

The company's Victoria office monitors more than a dozen sewage outfalls a year.

During a mandatory inspection in April, Mr. Clarke and another diver examined Sooke's sewage pipe, which reaches an ocean depth of 30 metres in the relatively clean, brisk-moving waters of Juan de Fuca Strait.

A video they made shows an underwater world of waving plants and darting fish in what had been a barren zone.

Attached to the outer cement blanket that keeps the pipe in place are plants such as kelp and other seaweeds. Sea cucumbers, sea stars, snails, crabs and other invertebrates mosey around. Mr. Clarke also spotted a fearsome-looking juvenile wolf eel.

Kelp greenling, quillback and copper rockfish, and most notably, lingcod - a fish much prized by anglers - have also taken up residence in the large gap between the cement ballast and the plastic sewage pipe.

"Now an artificial reef has developed, filling the length of the pipe. It's a structure that will support egg habitat," said Epcor's Ms. Wetmore.

Of significance is that lingcod have colonized the pipeline and are depositing eggs there.

"Any time you see a place where they like to spawn, that's a place you want to protect," Mr. Clarke said of the closely monitored species, which is found on the North American West Coast and is difficult to establish.

"In this case, a manmade structure is helping lingcod to propagate."

According to ongoing research by the Vancouver Aquarium, Strait of Georgia lingcod stocks have fallen to between 7 per cent and 22 per cent of what they were 100 years ago, and their numbers continue to decline around the West Coast.

Department of Fisheries and Oceans spokesman Dan Bate said creation of new habitat for lingcod is a "positive" step.

While B.C.'s West Coast has more than 100 marine outfalls, most originating at major cities or pulp mills, Mr. Clarke estimated that perhaps a dozen have brought about robust marine habitats.

Mr. Clarke predicted that when he dons his diving gear in about four years for a follow-up inspection, Sooke's pipeline will be encrusted with more life forms and support even greater numbers of invertebrates and fish.

"This is a great story. That's not to say build pipelines all over the place to help fish, but there are benefits."

At the end of the pipeline, the treated sewage is released via diffuser ports. The "virtually transparent water" rises rapidly to the midwater level and is quickly assimilated into the ocean, Mr. Clarke said.

Added Ms. Wetmore: "The marine environment is better than anyone expected."