Blue-Green Algae - Frequently Asked Questions

Eutrophication is the enrichment of a water body with excess nutrients. This can lead to a proliferation of blue-green algae in a waterbody. It can also lead to very low dissolved oxygen levels which negate the ability of fish and other aquatic organisms from surviving in such a water body.

Blue-green algae growth is relatively common in many urban lakes on Vancouver Island. In the case of Quamichan Lake, human activity since the turn of the last century has led to Quamichan Lake becoming eutrophic. Blue-green algae has been observed on Quamichan Lake as far back to the 1950s.

What is blue-green algae?

Blue-green algae are microorganisms called cyanobacteria. This means they are photosynthetic prokaryotes (they use energy from the sun to create their own oxygen). Blue-green algae are tiny plants that can bloom to cover entire lake surfaces and produce microcystin toxins. These microcystin toxins are harmful to people, pets, fish, and other wildlife.

Why is blue-green algae growing in Quamichan Lake?

Because blue-green algae is a photosynthetic prokaryote (we can think of it like a tiny plant), under ideal lake conditions it will grow quickly and outcompete other forms of life. Quamichan Lake is considered hyper-eutrophic (overly enriched with nutrients) and has ideal conditions for the proliferation of blue-green algae. Phosphorus is the main nutrient that facilitates the proliferation of blue-green algae. Phosphorus is present in the nutrient-rich sediment at the bottom of the lake and in the run-off that is entering the lake.

Are there methods for controlling blue-green algae growth?

There are many different methods that can be used to reduce nutrient concentrations, increase dissolved oxygen in the water, reduce water temperature. All of these methods come with varying degrees of involvement and cost. Because of this, it is necessary to collect some baseline data in order to ensure that the proposed remedial actions are appropriate for the scenario on a given waterbody. Currently, North Cowichan is working with a local consultant and BCIT's Ecological Restoration Program to determine the best combination of remediation options to improve lake health and ultimately eliminate the presence of blue-green algae.

Who is responsible for improving conditions in the Lake?

The bottom of Quamichan Lake is owned by a private landowner. Water resources in BC are currently under the mandate of the Ministry of Forests, Lands and Natural Resource Operations (FLNRO). As such, the Municipality has no jurisdiction on the lake. Despite this, the Municipality understands the importance of this lake to residents and First Nations. Residents use Quamichan Lake for various forms of recreation in addition to it being an important resource for local wildlife. In light of this, Council has directed staff to research some options that could improve the health of the Lake with the intent of attracting support from higher levels of government.

Is this a problem in other nearby lakes?

According to Island Health, blue-green algae is present in many urban lakes on Vancouver Island and the Gulf Islands. The level of presence of blue-green algae in a lake can vary dramatically dependant on the environmental conditions present in and around a lake. Some examples of blue-green algae outbreaks in the area are St. Mary Lake on Salt Spring Island and Elk Lake in Victoria.

Is North Cowichan testing the lake water for toxins and blue-green algae?

Yes, the Municipality is conducting testing in the Lake. However, the presence or absence of toxins can vary at any given location or time so the testing methods available are not a reliable means of determining whether or the water is harmful at a particular location or time. Furthermore, weather, boat traffic, and other environmental factors can move algae and toxins around the lake unpredictably. For this reason the Municipality has been advised by Island Health to place permanent signage at access points around the Quamichan Lake in order to advise the public of the ongoing potential for exposure to toxins. 

Is it safe to recreate on the lake?

Island Health is responsible for advising the public as to whether or not a particular waterbody is safe for use by the public. Those who are recreating on or around Quamichan Lake should be advised of Island Health’s Public Action Points relating to cyanobacteria. 

Where can I report observations or information about Quamichan Lake?

You can report directly to the environmental department at North Cowichan by emailing: