Atop the waters of Elk Lake, rowers train, racing back and forth, sometimes swimmers dip in from adjacent beaches and deep below, oxygen bursts in tiny bubbles in a bid for balance.
The streams of oxygen come from a diffuser hose at the end of a one-kilometre pipe out to the deepest part of the Saanich lake in a bid to eliminate deep-water oxygen depletion. And it’s working, albeit slowly, according to a Capital Regional District report to the parks commission on June 25, which outlines numbers derived from 2024 monitoring.
The lake is prone to blooms of blue-green algae, or cyanobacteria, caused by nutrient buildup at the bottom that accumulates. As microorganisms break down, they deplete oxygen and release phosphorus, which makes its way to the surface and feeds the algae.
Studies have shown that in Elk Lake, external sources account for 30 per cent of the nutrient load, the other 70 per cent is internal, accumulated over the past decades.
The oxygenation system targets that 70 per cent, diffusing high-purity oxygen into the deepest part of the lake to help reduce oxygen depletion, which keeps most of the phosphorus bound in the lake bottom sediments.
Goals are to eliminate deep-water oxygen depletion (anoxia), decrease internal phosphorus loading, maintain suitable cold-water fish native habitat and reduce the frequency and duration of algae blooms.
Deep-water oxygen levels improved last year with a shorter anoxia period of two months as opposed to five months in previous years. Deep water phosphorus dropped 80 per cent compared to previous years.
On the flip side, average deep-water temperatures were significantly higher at 12.5C than in previous years (average 8C) but remained below 15C. Algae blooms also continued and were longer-lasting than in previous years.
A significant bloom that prompted cancellation of the swim portion of the Ironman in May appears to be receding, the committee heard.
The blue-green algae blooms persisted throughout 2024 due in part to ideal environmental conditions for growth, such as heavy rainfall in July and August, warm temperatures and stable winds. So far this year, bloom conditions across the region and province have been some of the worst on record, the parks committee heard.
“Overall, findings highlight the need to continue addressing all nutrient sources impacting lake health through the operation of the oxygenation system and actions outlined in the Elk/Beaver Lake Watershed Management Plan,” the report states. The management plan includes working with Saanich and Central Saanich on external impacts.
Installed in late 2023, the oxygenation was fully commissioned in March 2024. In 2024, it cost $165,000 to maintain the $1.6-million system, including electricity, maintenance, water quality monitoring, expert consultation and staff time. Those costs are anticipated to be $175,000 this year.
Find the full report on the parks committee agenda online at crd.ca.
