Surber. — Biological Surveys in Minnesota. 227 



wood forest around the headwaters of all the tributaries and the 

 drainage of considerable marsh areas, so that the changes here 

 brought about are particularly noticeable, and will be spoken of 

 more fully in another paragraph. Investigations in the southern 

 quarter of the State show a reduction of the water table of approxi- 

 mately 4 feet during the past 60 to 70 years. While the time de- 

 voted to any particular system has been, necessarily, limited, it is 

 believed the results accomplished are worthy of record as adding 

 very materially to a correct understanding of present-day conditions 

 and the problem of meeting these conditions in the future. 



As a result of careful study of the conditions affecting the 

 aquatic life of state waters, the following cardinal principles in- 

 volved in their examination naturally present themselves : 



1. Obtain an accurate description of the body of water and 

 locate it definitely on a map drawn to scale. 



2. Determine the approximate flow of springs and all sources 

 of supply. 



3. Determine the amount and nature of the animal and plant 

 life of the waters and their suitability for maintenance of fish life 

 under existing conditions. 



4. Determine the pollution of the waters — its extent, and the 

 probable effect on aquatic life. 



5. Study the geographical features of the region, their rela- 

 tion to the permanence of the water supply, any immediate changes 

 now taking place and the probable effect of such changes on a 

 continuance of the existing conditions. 



6. Study the effect of flood waters on the plant and animal life ; 

 active erosion and its effect. 



7. Ascertain, if possible, past conditions of the waters. 



8. Report on contemplated drainage of marshes, wet prairie 

 uplands, lakes, etc., in their relation to permanence of the present 

 water supply. 



9. Definitely locate the best roads by which the waters are 

 accessible. 



The value to the department of working under these principles 

 grows more and more apparent as the work progresses. 



The change in conditions affecting our water supply in the 

 southeastern counties has been brought about not so much by 

 actual drainage, as we usually accept it, but more indirectly by 

 deforestation and destruction of the surface-absorbing strata of 



