This summer there were a number of wildfires both around Shuswap and Mara Lakes (Two Mile fire near Sicamous, Hunakwa Lake and Crazy Creek fires at the head of Anstey Arm), as well as fires in the tributary watersheds (White Rock Lake fire in the Salmon River drainage, Momich Creek fire in the upper Adams Lake drainage as well as fires adjacent to Mable Lake and in the Eagle River drainage). At the recent Shuswap Watershed Council Meeting the members started a conversation on how these fires could affect the water quality of the lakes in the Shuswap and Mara Lakes watersheds.
Using information available in the literature, there are a series of potential events that could result in changes to water quality:
- Wildfires do increase the susceptibility of watersheds to both flooding and erosion. In the relatively steep terrain surrounding the lakes, especially during spring snow-melt, there can be increases in both the rate and volume of runoff from the burned areas resulting in an increase in erosion and the subsequent deposition of fine and coarse sediment in the lakes. While this erosion is a naturally occurring process, the increased rate of erosion resulting from the burning of trees and the understory of shrubs, mosses and other woody debris that accumulates on the forest floor that normally retards the rate of runoff.
- As many of us experienced, wildfires generate and distribute ash over a wide area. During fall rain storms and the spring runoff, much of this ash will also be eroded and end up in the streams and lakes.
- The ash and other sediments can carry greater quantities of algae-promoting nutrients and even quantities of heavy metals into the lakes from the burned off areas.
As indicated above, many of these effects are tied to rain and snow accumulation in the burned off areas and especially to the rate of snow melt in subsequent years following the fires. These effects will also be mitigated by the rate of regeneration of shrubs, grasses and other plans in the burned areas in the years following the wildfires. Additionally, given the geographic size of our lakes and the local nature of the fires some of these effects may only be experienced near to the burned areas of the watersheds. However, if you depend on the lakes for your water supply, some caution and perhaps extra testing to make sure the water still meets drinking water guidelines may be wise.
Click here for link to HealthLinkBC article on Wildfire: Its Effects on Drinking Water Quality.
SWOA will continue to review the available literature on the water quality effects experienced elsewhere and report on these findings in our newsletter.