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1. Introduction

The South Thompson River, in the Southern Interior of British Columbia, begins at the outlet of Little Shuswap Lake, and flows southwest and west for 60 km before it converges with the North Thompson River at the City of Kamloops (Figure 1). It has a drainage area of approximately 16,200 km2 and a mean flow of 300 m3/s. The South Thompson River comprises about 40% of the flow of the Thompson River after the convergence with the North Thompson River (Nordin & Holmes, 1992), and ultimately drains into the Fraser River at Lytton. Water quality data for the South Thompson River were acquired at a monitoring station at Kamloops; stream flow data were acquired at a monitoring station near Chase.

The South Thompson River is an extremely important habitat for many fish species, with the well-known Adams River salmon run each summer and fall, and native species such as rainbow trout and Rocky Mountain Whitefish year-round (Nordin & Holmes, 1992). Besides the use as a habitat for many aquatic species, the designated water uses of the South Thompson River include agricultural irrigation, livestock and wildlife watering, domestic water supply, industrial use, and a significant amount of outdoor recreation such as swimming, fishing, camping, and boating. Non-point discharges provide the largest human contribution to water quality contamination in the South Thompson River, with land use activities, particularly cattle operations and forest activities in Chase Creek, probably having the greatest influence (Nordin & Holmes, 1992; Holmes, pc 1997).

The flow of the South Thompson River (Figure 2) was measured at Environment Canada site BC08LE031 near Chase (latitude 50° 45' 54" N by longitude 119° 44' 25"), and is plotted in Figure 2. The provincial water quality sampling station is located downstream from this site, at Kamloops, just before the confluence with the North Thompson River (latitude 50° 40' 46" by longitude 121° 19' 24"). Water quality monitoring began in 1973 and has been about monthly, with some gaps during the 1980's. The data are stored on the province's Environmental Monitoring System (EMS) database under site number 0600135. This report assesses the data between 1973 and 1997. The water quality data are plotted in alphabetical order in Figures 3 to 38. Other water quality stations within the Thompson River watershed include: the North Thompson at North Kamloops (Brewer & Webber, 1997b), the Bonaparte River near mouth (Brewer & Webber, 1997a), the Nicola River at Spences Bridge, the Salmon River at Highway #1 (Lilley & Webber, 2001), and the Thompson River at Spences Bridge (Webber et al., 2000).

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