234 American Pisheries Society. 



facilitates tremendous erosion at every flood. In most of the 

 streams of southeastern Minnesota the lighter surface soil is 

 carried down and deposited as a thick mass of silt over the bot- 

 tom, often entirely obliterating all traces of the rocky bed, and 

 covering it like a blanket. This has had the effect of smothering 

 out the clear water Entomostracans, Gammarus, and such aquatic 

 insect larvae as the caddis-fly during the period of hot weather 

 extending from the last June floods through to October, as dur- 

 ing this period cattle, hogs and sheep, great herds of which are 

 pastured along the banks with free access to the stream, keep the 

 water in constant agitation by standing most of the day in it ; and 

 during a season of the year when such streams were naturally 

 most clear, they produce a condition of intense roiliness, in which 

 some small aquatic life can not exist, and in which fishes will 

 not remain, if we except undesirable species as the carp for 

 instance. 



If a stream is thus divested of the natural food supply for the 

 smaller fishes, it seems hardly advisable to attempt to reintroduce 

 even adult fishes in its waters, as it is only a question of time 

 until they will either be caught or desert the stream in search of 

 food and clear water ; and since no food exists for their progeny, 

 even though they spawn in great numbers, it would be the height 

 of folly to attempt to introduce fry into such streams. Many 

 streams in southern Minnesota are found to have reached this 

 condition, and while from casual observation, they have the ap- 

 pearance of being suitable for trout, on more careful examination 

 they are found to be absolutely devoid of small animal life. 



BARNYARD POLLUTTON. 



Ordinarily it has been found that barnyard pollution has but 

 little effect on most streams, the most pronounced effect being 

 noted in the case of springs with a comparatively weak flow (50 

 gallons or less) situated in a barnyard which drains directly 

 into it. In the case of large springs this pollution seems to have 

 little bearing on the aquatic life, an example of this kind being 

 the large spring about a mile east of Spring Valley, coming out 

 from underneath a barn and continuously frequented by ducks, 

 geese, hogs and cattle; a few trout exist here apparently in the 

 best of condition, but in this case the heavy growth of water 

 cress apparently purifies and balances the water. On the other 



