30 NORTIIERxX FISHES 



amounts of carbonates in solution. The cold underwaters become 

 stagnant and deficient in oxygen for at least part of the year, and the 

 fish are therefore confined in summer to the warm surface waters. 



A number of large lakes in central and northern Minnesota, such 

 as Upper Red Lake and Lower Red Lake, Leech Lake, Mille Lacs, and 

 Cass Lake, are of this same type, though relatively shallow. The.y are 

 from 35 to 40 feet deep and from 8 to 15 miles across, and consequently 

 they are exposed to much wind and wave action. The wave action pre- 

 vents bottom stagnation and makes the bottom available to fishes 

 everywhere throughout the year. Walleyes are the dominating fishes of 

 these large lakes. Perch, northern pike, suckers, and many other species 

 are common. Sunfishes, bass, and crappies are not common except in 

 bays. The majority of the larger lakes of central Minnesota are of this 

 type, with its several variations. They are located in areas where the 

 soils are fertile and therefore are sometimes surrounded by agricultural 

 land. 



The fourth type is the bass, crappie, and sunfish lake. This type of 

 lake is small, but may have numerous bays and inlets. It is rich in 

 organic matter and has large amounts of vegetation. The waters con- 

 tain relatively large amounts of carbonates. The shores and bottoms 

 are generally mud and sand. This type is usually over 20 feet deep, 

 and a few exceed 100 feet in maximum depth. When the lakes are deep 

 enough, bottom stagnation with loss of bottom oxygen occurs. Since 

 large areas of bottom are inaccessible, the deep lakes of this type are 

 not as productive as some of the shallow ones. Bass, crappie, and sun- 

 fish lakes are found in most of Minnesota and Wisconsin, but rarely in 

 the northeastern corner of Minnesota. Northern pike, suckers, perch, 

 and other species are present in most of them, in addition to bass, 

 crappies, and sunfishes. 



Many Minnesota and Wisconsin lakes are a combination of the last 

 two types — the second kind of walleye lake and the bass, crappie, 

 and sunfish lake — and are suitable for all these species. They are large 

 and have many bays and inlets, thus virtually combining the condi- 

 tions of both small and large lakes. 



In Michigan, parts of Wisconsin, and to a very limited extent in 

 Minnesota, there is another type of lake suitable for smallmouth bass. 

 This type is a small, shallow, or only moderately deep, lake with rocky 

 shores. Little is known about this type of lake in Minnesota. 



The last type consists of the prairie lakes in the southwestern and 

 central parts of Minnesota and also in the Dakotas. These are hard- 

 water, fertile lakes, with rich mud bottoms and shores supporting 

 abundant aquatic vegetation. Most of them are shallow, ranging from 

 6 to 20 feet in depth. This type of lake is largely inhabited by bull- 

 heads, buffalofish, carp, and sometimes walleyes and other game fishes. 



