- 31 - 



expected pattern. Mercury in the edible tissue of smaller classes of 

 walleye (25-35 cm) rapidly declined from a median concentration of 0.85 

 milligrams per kilogram (mg/kg) in 1979 to 0.14 mg/kg in 1983. Likewise, 

 the mercury concentration in larger fish (35-50 cm), while remaining 

 higher than the smaller fish, declined from 1.32 mg/kg in 1979 to 0.42 

 mg/kg in 1984 . Mercury concentration of Cookson Reservoir white suckers 

 {Catastomus commersoni) was low (median 0.25-0.29 mg/kg) and unchanged 

 from 1979 to 1983 (Kruskal-Wallis 2-sample test, p=0.61). Munro (1985) 

 also reported on several species of "forage fish", such as brassy minnow 

 (Hybognathus hankinsoni) and less than one year old carp (Cyprinus 

 carpio) and suckers. Values for these three fish species ranged from 

 0.03 to 0.25 mg/kg. 



Other Water Quality Variables 



Table 3 contains a summary of excursions, for the period 1981 to 1990, to 

 the multi-purpose water quality objectives for the East Poplar River at 

 the International Boundary. There were no exceedances of the objectives 

 recommended by the IJC for TDS and boron. The following exceedances were 

 observed for the objectives recommended by the International Poplar River 

 Board to the IJC: 



Parameter 



Sampling 

 Date 



Agency 



Dissolved aluminum 

 Dissolved oxygen 

 Dissolved oxygen 

 Dissolved oxygen 

 Dissolved oxygen 

 Total zinc 



June 19, 1984 Environment Canada 



July 15, 1988 USGS 



Jan. 11, 1989 Environment Canada 



Feb. 8, 1989 Environment Canada 



March 6, 1989 Environment Canada 



April 15, 1982 USGS 



