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Vancouver may need to dig deep to save Beaver Lake in Stanley Park

Plans are being readied to remove thousands of tonnes of sediment from the lake in the heart of Vancouver’s Stanley Park.

Plans are being readied to remove thousands of tonnes of sediment from the lake in the heart of Vancouver’s Stanley Park.

Beaver Lake will fill in completely with sediment by 2020 without intervention, in part due to the presence of fragrant water lilies: a fast-growing foreign invasive plant. The lake’s proximity to the causeway road and walking paths is also accelerating the accumulation of inorganic debris.

“It’s been a manhandled park in many ways, but it is still a great place to see native plant and animal species and natural systems at work,” said Patricia Thomson, executive director of the Stanley Park Ecological Society.

Consultant AquaTerra Environmental has completed an assessment of the lake, its wildlife and vegetation and developed options for restoration. Two open house meetings are planned this month to present the options and gather public input.

Park board officials and the SPES have paid particular attention to the results of hydraulic dredging in Burnaby Lake, which was accomplished under strict environmental standards, according to the Society’s 2010 Ecological Action plan.

The plan identified the lake’s infilling as a top priority for restoration to halt “unacceptable loss of biodiversity and esthetic amenity.”

The forest environment and terrestrial wildlife were rated in fair condition, but the park’s aquatic environment is in serious decline, said Thomson. During the summer months, only a few patches of open water remain, with much of the lake’s original 6.7-hectare area covered with grassy humps and shrubs and floating weed mats.

Complicating the restoration plan is the return of beavers to Beaver Lake, five of them in all.

On one hand, the open water that does exist in Beaver Lake is maintained by the beavers around their lodge. But the industrious rodents also continually dam the outflow creek in an effort to further flood the lake, threatening the blue-listed cutthroat trout, a vulnerable species that needs steady water flow to survive.

Municipal water keeps the lake topped up and feeds the stream, but the drainage outlet has to be cleared of wood and mud regularly.

Planning is underway to restore the creek as viable salmon and trout habitat using funds from a creative sentencing fine levied against Kinder Morgan for a 2007 oil spill.

But creating an environment that will support salmonids and spawning may require the lake to be deepened.

The lake was last dredged in 1929, the beginning of a decade of road and path building that physically altered the area. Fragrant lilies were introduced in celebration of the 40th Jubilee of Dutch Queen Wilhelmina in 1938, the same year the causeway was completed.

Another significant human intervention is virtually assured.

“In 2011 the park commissioners agreed that to do nothing would be unacceptable,” said Thomson, explaining that the aquatics systems and riparian area is just to important to the park’s biodiversity.

“I don’t think that the decision will ultimately be to dredge the entire lake,” she said. “There will be different prescriptions throughout the lake.”

A bog on the lake’s south side will likely remain relatively untouched. The society has been removing hemlock trees and other plants that were overgrowing the bog and plans are in place to build a boardwalk that will allow better public access.