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f predators come ir0ih -.(it: it fuzCayc \ui at v ? `- ." --. - . Tn rainFj?+w i? tan .. ma *?i trout. the uptake of DDT complex from food was 2.5r: times that from water. Materials and Methods The objective of this study was to sample a large area of the Grand Valley for organochlorine-pesticides which may have accumulated in fish tissues. Based on previous studies it was expected that toxaphene would be found. Most of the streams draining agricultural areas from east of Grand Junction to Mack, Colorado were sampled, although not all of them produced fish. The sampling sites chosen were low in the drainages usually within a mile of the Colorado River. Fish were collected at 16 sites, all of which were located on streams draining the north side of the valley except for four on the Colorado River and one at Highline Reservoir. Fish collections were made from August 6 through 10, 1984 during the irrigation season. Fish were not numerous in the creeks and drains which flow into the Colorado River-. The species of fish available were the ones collected, and only those over 100 cm long were kept. The numbers of fish, species, and locations are summarized in Table 2. One method of collection was to tape a firecracker (M-80 type) onto a stone and allow one or more to explode in a pool or reach, and to recover stunned or dead fish which drifted to the surface or into a seine positioned downstream. On the Colorado River and in Highline Reservoir, electroshocking from a boat was the method used to collect fish. In previous years, fish were collected by electroshocking from the bank but equipment problems and water quality did not allow its use in this study. All three methods were effective. The Colorado Division of Wildlife provided most of the equipment and personnel for the project. Immediately after collection, the fish were wrapped in aluminum foil, bagged in plastic, identified with tags. and cooled with dry ice. At the end of each day, all fish were transferred to a freezer. Twenty-four fish from Highline Reservoir and the Colorado River were .sent to the Colorado-Department of Health for filet analysis. The rest, 59 fish, were submitted to the Columbia National Fisheries Research Laboratory for whole fish analyis by capillary gas chromatography for organochlorine pesticide residues. Actual sample analysis was done by Hazleton Laboratories America, Inc. of Madison, Wisconsin. Levels of detection were 1.0 ppm for toxaphene, 0.1 pom for PCB and 0.01 for other organochlorine contaminants. Sample wet weight, percent lipid, and chlorinated insecticide residue on both a wet and lipid basis were reported. Sample weights were about 25 grams. Quality control consisted of duplicate runs on seven samples; percent recovery determination was performed 3 times; two blanks were run. 4