Bluewater Creek? Let us look first at the creek above 

 the diversion ditches where the water is cool and 

 clean. In this part of the stream, one acre of stream 

 produced over 4,000 trout and only 40 suckers. This 

 is good trout water. Below the ditches that return 

 irrigation waste water, Bluewater Creek is warm and 

 muddy. Here, we find only 80 trout and over 12,000 

 suckers, dace and minnows in one acre. Obviously, 

 this is not good trout water. 



In upper Bluewater Creek, the average daily silt 

 or sediment concentration was a low 20 parts per 

 million. The lower part of the creek receives silt from 

 irrigation waste water ditches. Here, the average 

 daily silt concentration is eight times as great as in 

 the upper part of the creek. For the most part, the 

 high concentrations of silt in the lower part of the 

 creek occurred during the irrigation season. 



A comparison of stream flows in the creek above 

 and below the diversion ditches show that fish below 

 diversions have an unstable water supply with low 

 flows during the irrigation season. What effects do 

 these low flows have on water temperatures? In 

 July, the average maximum monthly temperature 

 was 72° F., well within the limits for trout. Below the 

 ditch, the average maximum monthly temperature 

 was 81° F., higher than ideal temperatures for trout. 



The Bluewater Creek study was initiated to dem- 

 onstrate how agricultural pollution — stream silt 

 accompanied by low flows and high water tempera- 

 tures — reduce the capacity of a stream to produce 

 trout. By comparing the fish populations with silt 

 concentrations, stream flow, and water temperature 

 in two areas, we can see that agricultural pollution 

 changes Bluewater Creek from a trout stream in the 

 clean water areas to a rough fish stream in the silty 

 areas. 



Specifically, how does agricultural pollution harm 

 trout? We know that trout deposit their eggs in 

 stream-bed gravel. In order to hatch, the incubating 

 eggs need high concentrations of oxygen and enough 

 water to wash away waste products given off by 

 growing trout eggs. Large amounts of silt settling on 

 riffle areas where eggs are incubating clogs up the 

 gravel. In a sense, the eggs are smothered by silt. 



We buried live eggs in the gravel in both the 

 clean and silty parts of Bluewater Creek. Approxi- 

 mately, 1,500 eggs were incubated in the unsilted 

 part; 6,000 in the silty part. 



In the clean part of the stream, 98 per cent of the 

 eggs hatched successfully. In the silty part of the 

 stream not one of the eggs hatched. A careful exami- 



nation of the dead trout eggs revealed the death- 

 dealing agent — a layer of silt covered the eggs. 



Our study shows how agricultural pollution with 

 high silt concentrations accompanied by low flows 

 and high water temperatures harm wild trout. The 

 Montana Fish and Game Department feels that agri- 

 cultural pollution should be recognized along with 

 municipal and industrial pollution as a detriment to 

 outdoor recreation in Montana. We want to empha- 

 size that agricultural pollution is not limited to a few 

 streams, rather it is a statewide problem in Montana. 



A detailed survey was conducted on Bluewater 

 Creek. The objective was to study the relationship 

 between stream sediment and trout egg incubation. 



Five sampling stations were established in Blue- 

 water Creek to measure sediment concentrations and 

 discharge. In the vicinity of the sediment-discharge 

 stations, man-made redds were constructed with 

 sorted gravel. Eyed rainbow trout eggs in hatching 

 boxes were introduced into the redds. Periodically, 

 the Mark VI standpipe apparatus was used to meas- 

 ure intragravel dissolved oxygen and intragravel 

 apparent velocity within the redds. The sampling 

 stations with low sedimentation rates, responded 

 with high intragravel dissolved oxygen rates; high 

 intragravel seepage rates (apparent velocities); and 

 low trout embryo mortality. Conversely, the sampling 

 stations with high sediment rates, responded with 

 low intragravel dissolved oxygen rates; low intra- 

 gravel seepage (apparent velocities) rates; and high 

 trout embryo mortality. 



Stream survey work was done on the Tongue, 

 Clarks Fork, and Stillwater Rivers. Kersey Lake was 

 also surveyed in preparation for a rehabilitation 

 project. 



A stream channel alteration inventory was com- 

 pleted on the Little Big Horn River. Over one-half of 

 the river channels had been altered. Channel re- 

 locations resulted in 17 miles of new, straightened 

 channel which diverted the water from 36 miles of 

 former, meandering channel. Diking and channel 

 clearance altered five miles of river channel and six 

 miles of river bank had been riprapped. Charuiel 

 alterations on Montana streams have been accom- 

 panied by drastic decreases in trout populations, and 

 results in a serious drain in our stream fishing re- 

 source. 



Rock Island Lake and Crater Lake were rehabili- 

 tated during the biennium. Both lakes contained 

 suckers and chubs which were probably introduced 

 by fishermen using small fish for bait. Both species 



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