Executive Summary

The Unuk River is located in northwest British Columbia, flowing southwest to Alaska and the Pacific Ocean (Figure 1). Proposed and active mining projects are located within the Unuk River watershed. Also, the Unuk is important to sport and commercial fishing, mainly in the Alaskan portion of the river.

This report assesses water quality data collected at the monitoring station 3 km upstream from the Alaska border and 65 km northwest of Stewart, B.C. Water quality samples were collected between 1991 and 1993 by Environment Canada. Flow was measured at a Water Survey of Canada flow gauge at the water quality monitoring station.

We concluded that:

· Not enough data were available to comment on trends in water quality, although a slight downward trend in pH was apparent.
· High metals and non-filterable residue occurred together. This suggests that metals were in a particulate form, probably not biologically available, and would be removed by the turbidity removal needed before drinking.
· Total aluminum, cadmium, chromium, copper, iron, lead, manganese and zinc, apparent colour, non-filterable residue and turbidity values did not meet various water quality criteria at times due to high levels of suspended sediment in the water during freshet.
· Copper levels exceeded the aquatic life criteria at all times, suggesting a naturally high copper mineralization in the watershed.
· The river had a low sensitivity to acid inputs.
· Hardness levels were generally below the optimum range for drinking water in the summer and within the optimum range in the winter.
· Treatment to remove turbidity (plus disinfection) would be necessary before the water was used for drinking.
· The water was cool enough to be aesthetically pleasing for drinking, but too cold for water-contact recreation such as swimming.

We recommend that reactivation of water quality monitoring be considered for the Unuk River near the U.S. border because:

· It is a trans-boundary river that supports an important fishery.
· There are active and potential mine sites within the watershed.
· The watershed is relatively small (1480 km²) and thus potentially sensitive to change.
· The existing baseline water quality record is short and sparse.
· The forthcoming road construction will improve access for the purpose of monitoring.