EFFECTS OF DDT SPRAY ON FISH AND AQUATIC INSECTS IN 

 GALLATIN RIVER DRAINAGE IN MONTANA 



By 



W. R. Bridges and Austin K. Andrews 

 Bureau of Sport Fisheries and Wildlife 

 Fish -Pesticide Research Laboratory 

 Denver, Colorado 



ABSTRACT 



The Swan Creek drainage was treated with DDT at the 

 rate of 1 .0 pound per acre as a part of a larger spruce 

 budworm control program. Although the plane didn't spray 

 within one-quarter mile of the stream, a level of 0.01 

 ppm of DDT was measured in the water samples taken 

 half an hour after the spraying. Tremendous numbers 

 of aquatic insects were killed or seriously affected. 

 Samples of these insects contained progressively larger 

 amounts of DDT, up to 11.0 ppm after 3 hours. Rain- 

 bow trout exposed in the stream for various periods up 

 to 96 hours suffered no apparent acute effects, but con- 

 tained as much as 0. 1 ppm of DDT in their tissues. 



The U.S. Forest Service conducted a 

 large-scale spruce budworm control program on 

 the Gallatin National Forest in Montana in July 

 1960. Approximately 60,000 acres of forest 

 land in the Gallatin River drainage were treated 

 with DDT (fig. 1). The Forest Service re- 

 quested the Fish -Pesticide Research Laboratory, 

 Denver, Colorado, and the Denver Wildlife Re- 

 search Center to make observations on the effects 

 of the spray on the fish and wildlife resources of 

 the area. This report deals with the work of the 

 Fish -Pesticide Research Laboratory in relation 

 to the spray operation . 



The time and personnel available required 

 that our efforts to quantitatively measure the ef- 

 fects of the spray be restricted to a relatively 

 small segment of the total spray area . Swan 

 Creek, a tributary to the Gallatin River, was se- 

 lected as the study stream . 



THE STUDY STREAM 



The mouth of Swan Creek is approximate- 

 ly 15 miles south of Gallatin Gateway, Montana 

 (fig. 1). The stream is about 20 miles in length. 



I o Gallatin Gateway 



GALLATIN SPRAY AREA 



SWAN CREEK SPRAY PLOT 



Figure 1. --General DDT spray area 

 and the Swan Creek spray plot, Gal- 

 latin National Forest, Montana, 1960. 

 Stippled portions denote areas sprayed. 



but only the lower 2 miles were included in the 

 spray plot. Swan Creek flows through a steep. 



1 



