Surber. — Biological Surveys in Minnesota. 233 



excellent trout stream. On the other hand the streams of the 

 reforested country south and east of this, previously mentioned 

 as having recuperated since 1894, are now among the best trout 

 streams in the State, for the dense cover along their courses tends 

 to preserve natural conditions of environment, and not only af- 

 fords shade and food in abundance, but also tends to preserve a 

 low temperature during the heat of summer. 



Similar conditions obtain in other parts of the State where 

 cut-over lands have reforested themselves ; and in northern Hub- 

 bard and southern Beltrami counties the streams have so recuper- 

 ated that it has been possible to introduce trout with marked 

 success in waters which had previously been uninhabited by any 

 species but pike, pickerel and suckers, the trout being unknown 

 in that region as a natural inhabitant. 



In abundance and variety of food supply for fishes many of 

 the streams in cut-over country, where not heavily fired, closely 

 approximate that of wild country, but as soon as the country is 

 divested of this second-growth and put under the plow its change 

 is remarkably rapid, and in an incredibly short time floods and 

 sun do their work and all small animal life disppears. In some 

 of the streams of the southern part of the State it has required 

 but 50 to 75 years to accomplish their ruin, even when the spring- 

 water supply was twice that of other sections, so that it can be 

 realized how rapidly it will be accomplished in a region where the 

 spring-water is limited, and that supply dependent on swamp- 

 seepage for its maintenance. 



THE INI^LUENCE OE A REDUCED WATER SUPPEY ON AQUATIC ANIMAI, 

 ElFE AND ITS BEARING ON POLEUTION. 



We can readily understand that with a reduced flow all 

 streams necessarily become more susceptible to pollution. This 

 pollution should be divided into actual sewage waste on the one 

 hand, and long-continued agitation by domestic animals during 

 periods of hot weather, of the accumulated silt bearing minor 

 sewage, on the other, the results, so far as afifecting fish-life, 

 being similar. 



While sewage pollution is regarded as most highly injurious 

 to fish life, there is considerable question if the silt carried down 

 from the uplands is not even more injurious in the more settled 

 districts, where intensive cultivation of former forested areas 



