MANAGEMENT OF WATERS 29 



water fishes. Minnesota lakes suitable for fish can be divided into at 

 least five t,ypes according to the species of game fishes for which they 

 are best adapted. Surveys of lakes in neighboring states have yielded 

 similar types. 



The first type is the lake trout lake. It is more or less infertile, with 

 much rocky bottom. The shore drops steeplj^, is almost entirely bedrock, 

 and is unproductive. These lakes are deep, with a maximum depth of 

 over 100 feet. The water in such a lake is low in both mineral and 

 organic content. Owing to the depth of the lake and its low organic con- 

 tent there is plenty of oxygen at the bottom. Although the surface 

 waters may warm up, the bottom waters are always cold enough for the 

 lake trout. Northern pike, suckers, tullibee, and sometimes walleyes are 

 also found in these lakes. These lakes are confined mostly to the border 

 region, from Lake of the Woods through the Superior National Forest, 

 and are located in areas of surface igneous rock, where the soils are low 

 in fertility and the drainage waters are very soft. 



In the same area there are some small lakes that have proved to be 

 suitable for stream species of trout. The waters are cold and msiy not be 

 over 40 feet deep. These lakes are usually fed by springs or cold bog 

 drainage. Brook, brown, and rainbow trout have been introduced in 

 these waters and have done very well. 



The second tj^pe of lake is one of two kinds in M'hich walleyes thrive. 

 It is difficult to determine the factors necessary for a walleye lake, but 

 walleyes apparently do best in lakes where they have plenty of range. 

 The only small lakes in which they thrive are those that have open 

 channels into other lakes, forming a chain. The first kind of walleye 

 lake is similar to the lake trout type. It has rather rocky shores and is 

 relatively infertile. In fact it has all the characteristics of a large lake 

 trout type except that it is too shallow for lake trout. Many of these 

 lakes are only 75 or 80 feet deep. The cold water below the thermocline 

 has insufficient volume to carry enough oxygen- through the summer 

 and consequently is not ideal for lake trout. Some contain a few lake 

 trout, many northern pike, and usually some suckers and perch, but 

 most of them did not originally contain walleyes. The walleyes have 

 been introduced and are thriving better in this type of lake than in 

 any other waters in Minnesota. Lakes of this type are located on rather 

 rocky soils in Lake and Cook counties. 



The other type of walleye lake is entirely different, being warmer 

 and quite fertile. This type is large, with sand and mud bottoms, sup- 

 porting abundant, submerged vegetation in the shoal waters. The lake 

 may range in depth down to 200 feet. Lakes of this type may be divided 

 more or less according to size and depth. In fact, some of the deeper 

 lakes in Minnesota are of this type, but they are not suitable for lake 

 trout because they are fertile and their bottoms are very rich in organic 

 matter. The waters are rather hard, for they contain relatively large 



