Why is Lake Omar green? (And some other interesting facts)
Shawnigan’s aquatic centrepiece, Lake Omar, has undergone many changes over the decades, and has been the focus of a major remediation project over the last year. Unrelated to that project, it is covered this fall with what appears from a distance to be a film of algae, but on closer inspection is in fact millions of tiny plants known as duckweed. Environmental Lead and Horticulturalist Ms. Patricia Hanbidge explains.
Lake Omar is a manmade pond that has been part of the Shawnigan campus for decades. It has had many uses over the years but now is a thriving ecosystem that supports a variety of life forms from tiny single-celled organisms to amphibians, crustaceans, fish, birds, mammals and reptiles.
To understand what is happening in this water body, we need to understand the succession of developmental stages. Lake Omar and Kaye’s Pond are catchment ponds that serve as reservoirs for water running downhill from higher-elevation areas on campus. When water levels are high, Lake Omar overflows into Hartl Creek, then Shawnigan Creek, and eventually the water enters the Pacific Ocean at Mill Bay. Where this water enters the ocean is the same spot where our salmon enhancement program begins – adult coho salmon make their way into the fish trap, and help them get by many impassable falls to their spawning grounds. Kaye’s Pond, meanwhile, flows into Shawnigan Lake.
A pond is a small, still body of water that is typically shallower than a lake, which allows sunlight to reach the bottom. The pond succession or ecological development of a pond can be a long process. It goes through stages of oligotrophic, mesotrophic and eutrophic development. As the vegetation grows and debris accumulates, the pond will gradually fill in and be transformed into a marsh and eventually a terrestrial ecosystem.
When a pond is young, it is at the oligotrophic stage of development. The water at this stage is clear and there are low nutrient levels. At the mesotrophic stage or middle life of a pond, more nutrients are present, debris accumulates on the bottom and submergent vegetation appears. At the eutrophic stage, the pond has reached mature development, the pond floor has accumulated organic matter (muck or sludge) and there is increased vegetation growth. Lake Omar is considered eutrophic and only through human intervention can be retained as a pond.
The vegetation both in and around the pond needs to be controlled. The micro-aeration system we installed in 2024 helps to naturally decrease the level of muck on the pond floor. This system gently aerates this organic layer and microorganisms can happily consume this formerly anerobic muck to reduce how much is present.
A “summer umbrella” of floating cedar logs has been installed on the lake, and will is being planted with a variety of plants that turns these logs, which were salvaged on campus, into a floating treatment wetland. The roots of the plants grow into the water and absorb nutrients and break down any contaminants through the natural biological process known as bioremediation. The plant roots also provide extensive surface area for microbes to grow, forming a slimy biofilm where most of the magic occurs. This type of treatment is used all over the world to purify and improve water bodies that may be contaminated with many products. The summer umbrella is a green infrastructure project that sequesters carbon, absorbs greenhouse gases and provides a unique habitat for insects, pollinators and many other creatures.
You might be wondering why Lake Omar is so green if all these wonderful things are happening. The green you are currently seeing on Lake Omar is duckweed. It is a tiny plant that is found on still, warm water that has high nutrient levels. It is not harmful, and you will see it dissipate soon. During August, the water lilies became infested with aphids and thus died back. For a period of a good month, they were not actively growing and so did not utilize nutrients. During this time, the level of water in Lake Omar continued to drop and the perfect conditions for duckweed occurred. The water lilies are now putting on new growth and will begin to absorb nutrients from the water. As the rains come and the water level rises, you will again see changes in Lake Omar.
Watch for more developments as Lake Omar is transformed. There are currently three young otters enjoying munching on the crayfish in the lake. This fall, as the water temperature gets cooler with the added input of rain and runoff, trout will be reintroduced to Lake Omar.
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Patricia Hanbidge is Shawnigan Lake School's Environmental Lead and Horticulturalist. She has worked extensively around the world, helping people develop food sovereignty, enhance food security, and build more sustainable communities.
We acknowledge with respect the Coast Salish Peoples on whose traditional lands and waterways we live, learn and play. We are grateful for the opportunity to share in this beautiful region, and we aspire to healthy and respectful relationships with those who have lived on and cared for these lands for millennia.
Shawnigan Lake School is an independent co-educational boarding school for ages 13 –18 on Canada’s beautiful Pacific Coast. Our diverse, interdisciplinary and innovative programming helps shape the next generation of global leaders.
