“Dead lakes” or “dead zones” are more common terms for hypoxia, which refers to a reduced level of oxygen in the water.
When it occurs, most marine life either dies, or, if they are mobile such as fish, leave the area.
According to David Karn, Spokesperson for the Ministry of Environment, Burns Lake has not been designated as a “dead lake.” The ministry of environment has sampled water in Burns Lake periodically every spring and summer.
For many years, however, residents in the Burns Lake watershed have noticed degradation in the quality and health of the lake.
In 1999, a group of concerned residents formed the Lakes District Watershed Enhancement Society (LDWES). The group was eventually disbanded due to a lack of members. In 2002, the LDWES assisted the provincial government in the creation of a draft management plan for the Burns and Decker Lakes watershed.
The report outlines residents’ main concerns including the “cultural eutrophication” of the lake.
Eutrophication is the process associated with the gradual built up of organic matter, nutrients and sediments in lake basins. Cultural eutrophication is a term used to describe the accelerated rate of the eutrophication process due to human settlement, clearing of forests, and development of farms within a lake’s watershed.
Residents and biologists claimed that water quality in the lakes was degrading as a result of land use in the watershed, mentioning the village sewage system, individual septic systems and agricultural, forestry, commercial and residential activities in the watershed.
Residents had also observed increased algal and macrophyte production, and a shift in fish species distribution. These are typical characteristics of lakes undergoing eutrophication.
In addition, residents identified that the social value of Burns and Decker Lakes had declined substantially over the years.
“The lakes are no longer as visually appealing, and aquatic plant growth is interfering with many recreational pursuits,” stated the 2002 report.
According to the ministry of environment, water clarity has been relatively poor at the sites where they have recently sampled.
Spring and summer “secchi depth” readings are less than two meters. Secchi depth is an indicator of water transparency; it’s the depth at which a black and white disk comes into sight after it has been lowered into the lake and then raised back up again.
According to Laura Hooker, Associate Professor of Biology for the University of British Columbia, a secchi depth reading of less than two meters is considered shallow.
“The Okanagan Lake, for example, is about seven metres,” she said. The Ministry of Environment also says Burns Lake has “naturally high concentrations of phosphorus.”
Most of the phosphorus in the lake is sourced from the Endako River. However, the Burns Lake sewage outfall was estimated to contribute 24 per cent of the lake’s phosphorus in 1998.
Since that time, the Village of Burns Lake has installed a phosphorous treatment system which is expected to have significantly reduced phosphorous input from sewage treatment.
Sheryl Worthing, Chief Administrative Officer for Burns Lake, said the village installed a phosphorous removal system at a cost of $ 200,000.00 plus engineering in 2004.
In addition, the village’s public works crew stopped weed control at Radley Beach prior to the 2002 report, likely due to a recommendation from the department of fisheries regarding damage to fish habitat.
The ministry of environment has sampled Burns Lake for a number of years as part of the provincial lake monitoring program. The sampling is done at two deep water locations in the lake identified as the east and west basins. The east basin is located near Deadman’s Island, and the west basin is located near the lake’s outlet river.
Other findings from the Burns Lake sampling include:
• Water in Burns Lake is replaced every 0.76 years, or approximately 1.3 times per year;
• During spring turnover, when the lake is mixed, the dissolved oxygen level at depth is high – over 10 milligrams per litre, in 2004 and 2015;
• In the late summer, oxygen levels below the thermocline can get relatively low – less than two milligrams per litre (August 2002). This level of oxygen will not support trout, but the fish will live in other parts of the lake where the oxygen is higher;
• It is common for lakes in Northern B.C. to mix in the late fall as temperatures cool; oxygen levels would be expected to increase at this time.
• Low oxygen levels may in the late summer may be attributed to decomposing aquatic plants. Bacteria that decompose plants use oxygen. In deeper unmixed portions of the lake where dead plants settle, oxygen can become low until the lake is mixed again in the fall and spring;
• Metal concentrations are below B.C. water quality guidelines and are not a concern.
The extent of available data is limited and is restricted to spring and summer. The lake will be sampled again in the late summer of 2015.
