narrow canyon within the boundaries of the 

 spray plot. Near the mouth of the stream the 

 elevation ranges from about 5,700 feet at the 

 valley floor to approximately 6,500 feet at the 

 upper limits of each side of the spray plot . 

 Swan Creek is typical of streams present in the 

 spray area . It is swift and practically devoid 

 of pool areas. The bottom is composed of boul- 

 ders and coarse rubble. At the time of the 

 spray the stream was high and running at a ve- 

 locity of 5 feet per second. The estimated flow 

 was 40 cubic feet per second. Water quality de- 

 terminations were: temperature, 47° F; pH, 

 8.0; and methyl orange alkalinity, 33 ppm. In- 

 vertebrate populations were moderately abun- 

 dant and anglers' creels contained brook, cut- 

 throat, and rainbow trout. 



THE SPRAY OPERATION 



Most of the spray plots were treated with 

 DDT at the rate of 1.0 pound per acre. Although 

 some plots along the Gallatin River were treated 

 at the rate of . 5 pound per acre, the Swan Creek 

 plot received 1 .0 pound per acre, sprayed from 

 a Ford tri -motor airplane. 



Pilots of planes were instructed not to 

 spray within one -quarter mile of the Gallatin 

 River and its main tributaries. Although pilots 

 carried out the instructions on the Swan Creek 

 plot and on other plots where spray operations 

 were observed, some of the toxicant spray did 

 reach the streams. An observer on the valley 

 floor could see the spray mist start rolling down 

 the sides of the canyon as it was applied. The 

 spray could not be seen on the valley floor, but 

 it could be detected by smell on Swan Creek and 

 on other plots where the canyon sides were 

 steep . 



The Swan Creek plot was sprayed on July 

 3, 1960, between 5:00 AM and 6:00 AM. Two 

 loads of toxicant were required to cover the area 

 sprayed. The plane flew parallel to the stream, 

 and sprayed a strip about 500 feet in width on 

 the upper slopes of each side of the spray plot. 

 The toxicant was not directly applied to the ma- 

 jor portion of the spray plot, but drifted down 

 to the lower slopes and to the stream. 



Spray cards to measure amounts of 



toxicant reaching the surface of the water were 

 placed at 8 locations at 400-yard intervals along 

 Swan Creek within the spray plot. The cards 

 indicated that essentially no spray reached the 

 water surface. The results of our study show 

 that in this instance the cards were not a reli- 

 able index; the toxicant did contaminate 

 the stream. 



EFFECTS OF THE SPRAY ON FISH 

 AND AQUATIC INSECTS 



The sampling of Swan Creek was designed 

 to determine the amounts of DDT in water, the 

 acute effects on fish and aquatic insects, and the 

 DDT residues in fish and insects. All samples 

 were collected at one sampling station located 

 near the mouth of Swan Creek (fig. 1). Later 

 our staff chemists conducted analyses for DDT 

 by the paper chromatographic method in our 

 laboratory at Denver . 



Amounts of DDT in the water 



Two water samples, one surface and one 

 subsurface, were collected from the stream be- 

 fore the spray and at 0.1, 0.5, 1.0, 1.5, 2.0, 

 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 10.0, 12.0, and 

 24.0 hours after the spray was applied. Sepa- 

 rate analyses revealed no difference in the DDT 

 content between surface and subsurface waters. 

 No DDT was found in the water before the spray. 

 Only a trace, less than 0.002 ppm, was detected 

 0.1 hour after the spray was applied. The 0.5 

 and 1.0 hour samples contained 0.01 ppm and 

 0.002 ppm, respectively. Samples collected 

 after one hour ranged from a trace of DDT to 

 none detected. Most of the DDT in the water 

 was apparently flushed from the Swan Creek area 

 within an hour of the termination of the spray ap- 

 plication. This is not surprising when one con- 

 siders that the stream was flowing approximately 

 3.4 miles per hour. 



Acute effects on aquatic insects 



Tremendous numbers of aquatic insects 

 were adversely affected by the DDT spray, as 

 indicated by samples of dead or morbid insects 

 drifting in the stream. A drift sample was ob- 

 tained by fishing a 40-mesh nylon net 10 inches 

 in diameter for 5 minutes . A mayfly nymph. 



