Water Stewardship Information Sources
| Citation | Pommen Water Quality Consulting. 2004. Water quality assessment of Cowichan River near the mouth (1985-2003). Prepared for BC Ministry of Environment. |
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| Organization | Ministry of Environment |
| URL | http://www.env.gov.bc.ca/wat/wq/quality/cowichan/cowichan.pdf |
| Abstract/Description or Keywords | The Cowichan River watershed is located in the southwest corner of British Columbia on the southeast coast of Vancouver Island. The headwaters are located in the Vancouver Island Mountains surrounding Cowichan Lake, and the river flows east to the Cowichan Bay estuary near Duncan. The water quality sampling station on the Cowichan River near the mouth is located two kilometres upstream from the Koksilah River and one kilometre downstream from the Duncan-North Cowichan treated sewage discharge. The river is one of the most important on Vancouver Island for recreational and commercial fish species, and is used for recreation and irrigation near the mouth. The main sources of contamination near the mouth are treated municipal sewage, fish hatchery effluent, agriculture, and urban development. This assessment is based on up to 19 years of water quality data during 1985-2003. The water quality trends identified below have not yet been confirmed by statistical analysis. CONCLUSIONS • The water was very soft with respect to hardness, but had a low sensitivity to acids. • The water quality objectives for ammonia, fecal contamination, lead, and zinc were attained. • Periphyton algal growth met the water quality objective on the one occasion when it was measured at the station in 1993, but a 1998 survey of the lower river found that the objective was exceeded downstream from the Duncan-North Cowichan sewage treatment plant outfall. There was ample nitrogen and phosphorus to support algal growth. • Phosphorus had a declining trend in 2002-03 due to waste abatement at the Duncan-North Cowichan sewage treatment plant. • Total copper exceeded the objectives occasionally during 1998-2003 due to elevated flow and turbidity, but dissolved copper met the objectives. • Chromium, cobalt, iron, and manganese occasionally exceeded guidelines for drinking water aesthetics and/or aquatic life, during winter high flows due to elevated turbidity. • Water quality objectives for dissolved oxygen were often not attained. • Water temperatures exceeded the guideline for cold-water fish species during the summer, when the water was warm enough for swimming. • Apparent increasing (deteriorating) trends in fecal coliforms, non-filterable residue, and turbidity were attributed to the increased sampling frequency during 2000-03. • Apparent decreasing (improving) trends in lead, molybdenum, and zinc were attributed to decreasing minimum detectable limits over time. |
| Information Type | report |
| Regional Watershed | Vancouver Island South |
| Sub-watershed if known | Cowichan |
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| Project status | complete |
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