The water quality graphs were inspected and erroneous values were removed. Metals such as chromium, copper, lead and zinc had high values between 1986 and 1991. This contamination was caused by the breakdown of preservation vial liners and lids. Environment Canada reported low pH values between 1986 and 1988 due to laboratory problems. Mercury data were not included in the report because all detectable values are believed to result from contamination during the collection and measurement process (Pommen, 1994). Quality assurance issues are expanded upon in the next section.