The North Thompson River originates in British Columbia's Rocky Mountain interior southwest from Valemount, flows south to Clearwater and McLure, and joins the South Thompson River at Kamloops to become the Thompson River (Figure 1). Approximately 300 km in length, the river is important for uses such as drinking water, recreation, aquatic life, wildlife, irrigation and livestock watering. Water quality is affected by agriculture, urbanization, and forestry, particularly in the southern section of the river downstream from McLure. There are no significant industrial or municipal discharges into the river. Other long-term monitoring stations on the Thompson River are South Thompson River at Kamloops and Thompson River at Spences Bridge.
In this report, nine years of data (1987-1995) obtained under the Canada - B.C. Water Quality Monitoring Agreement were assessed for trends and concerns in water quality. The 47 variables were graphed, and compared to water quality guidelines and to site-specific water quality objectives set by BC Environment.
The main conclusions of this study are:
· No environmentally significant trends were found.
· The site-specific fecal coliform objective to protect drinking water receiving only disinfection appeared to have been exceeded at times. Partial treatment and disinfection of drinking water are needed due to frequent high fecal coliform, E. coli and turbidity levels.
· Occasionally, levels of aluminum, copper, iron and zinc exceeding guidelines for aquatic life or drinking water have been observed in winter and fall, in association with low levels of non-filterable residue. Levels appeared to be naturally high in the river, since higher values during low flows have occasionally occurred since monitoring began in 1987, and since there were no significant industrial discharges into the river.
· Variables exceeding guidelines at times during spring freshet were aluminum, chromium, copper, iron, manganese and titanium. High levels occurred in conjunction with high levels of non-filterable residue and turbidity, suggesting that the metals were in particulate form, not biologically available, and would be removed by drinking water treatment needed to remove turbidity.
· Guidelines were consistently met for most of the sampled variables, including: barium, beryllium, boron, dissolved chloride, magnesium, nickel, molybdenum, ammonia, nitrate/nitrite, pH, specific conductivity, dissolved sulphate, and vanadium.
· The water was well buffered against acid inputs.