· There was weak evidence of an increasing trend in spring overturn total phosphorus during 1975-99. Total phosphorus values were above the upper guideline for aquatic life for 6 of 14 years, and above the guideline for drinking water and recreation for 10 of 14 years between 1975 and 1999.
· Chlorophyll a values were collected in 1980 and exceeded the guidelines for aquatic life, drinking water, and recreation.
· Phosphorus was the limiting nutrient for algal growth in Cusheon Lake.
· Increases in sodium, chloride, and specific conductivity indicated possible disturbances within the watershed.
· Total organic carbon values exceeded the guideline for raw drinking water. Chlorinating the water may produce trihalomethanes that exceed the drinking water guideline.
· The Capital Health Region determined that the public beach on Cusheon Lake was suitable for bathing between 1981 and 1995.
· True colour values exceeded the guideline for drinking water aesthetics in 33% of the samples from Cusheon Lake.
· Dissolved oxygen did not meet the guideline for protecting adult and juvenile salmonids from production impairment in 29% of the samples during 1974-94. The guideline for protecting adult and juvenile salmonids from moderate production impairment was not met in 2% of the samples during this period.
· Water temperature exceeded the drinking water aesthetics guideline at the deep station in Cusheon Lake in October 1980. The guideline may also have been exceeded during the summer months.
· Total calcium values show that the lake had a low sensitivity to acid inputs (the lake was well buffered).
· Total iron values exceeded the guideline for drinking water aesthetics and aquatic life in two samples collected in 1974.
· Total manganese exceeded the guideline for drinking water aesthetics in samples collected in 1993 and 1994.
· One extinction depth value measured in October 1980 did not meet the guideline for swimming and may indicate that the guideline was not met in the summer months when swimming would most likely have occurred.
· Turbidity exceeded the aesthetics objective for drinking water (with disinfection only) in 20% of the samples collected between 1974 in 1995. The drinking water health guideline was exceeded in 80% of the lake samples. The turbidity levels in the Cusheon Lake were such that treatment processes to remove it are required prior to drinking.