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The lakes of Iowa may be properly divided into two distinct classes. The first may be called drift lakes, having had their origin in the depressions left in the surface of the drift at the close of the glacial epoch, and have rested upon the undisturbed surface of the drift deposit ever since the glaciers disappeared. The others may be property termed fluvatile or alluvial lakes, because they have had their origin by the action of rivers while cutting their own valleys out from the surface of the drift as it existed at the close of the glacial epoch, and are now found resting upon the alluvium, as the others rest upon the drift. By the term alluvium is meant the deposit which has accumulated in the valleys of rivers by the action of their own currents. It is largely composed of sand and other coarse material, and upon that deposit are some of the best and most productive soils in the State. It is this deposit which form the flood plains and deltas of our rivers, as well as the terraces of their valleys.
The regions to which the drift lakes are principally confined are near the head waters of the principal streams of the State. We consequently find them in those regions which lie between the Cedar and Des Moines Rivers, and the Des Moines and Little Sioux. No drift lakes are found in Southern Iowa. The largest of the lakes to be found in the State are Spirit and Okoboji, in . . .
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. . . Dickinson County; Clear Lake, in Cerro Gordo County; and Storm Lake, in Bunea Vista County.
Spirit Lake.—The width and length of this lake are about equal; and it contains about twelve square miles of surface, its northern border resting directly on the boundary of the State. It lies almost directly upon the great watershed. Its shores are mostly gravelly, and the country about it fertile.
Okoboji Lake.—This body of water lies directly south of Spirit Lake, and has somewhat the shape of a horse-shoe, with its eastern projection within a few rods of Spirit Lake, where it receives the outlet of the latter. Okoboji Lake extends about five miles southward from Spirit Lake, thence about the same distance westward, and then bends northward about as far as the eastern projection. The eastern portion is narrow, but the western is larger, and in some places a hundred feet deep. The surroundings of this and Spirit Lake are very pleasant. Fish are abundant in them, and they are the resort of myriads of water fowl.
Clear Lake.—This lake is situated in Cerro Gordo County, upon the watershed between the Iowa and Cedar Rivers. It is about five miles long, and two or three miles wide, and has a maximum depth of only fifteen feet. Its shores and the country around it are like that of Spirit Lake.
Storm Lake.—This body of water rests upon the great water shed in Buena Vista County. It is a clear, beautiful sheet of water, containing a surface area of between four and five square miles.
The outlets of all these drift-lakes are dry during a portion of the year, except Okoboji.
Walled Lakes.—Along the water sheds of Northern Iowa great numbers of small lakes exist, varying from half a mile to a mile in diameter. One of the lakes in Wright County, and another in Sac, have each received the name of “Walled Lake,” on account of the existence of embankments on their borders, which are supposed to be the work of ancient inhabitants. These embankments are from two to ten feet in height, and from five to thirty feet across. They are the result of natural causes alone, being referable to the periodic action of ice, aided, to some extent, by the force of the waves. These lakes are very shallow, and in winter freeze to the bottom, so that but little unfrozen water remains in the middle. The ice freezes fast to everything upon the bottom, and the expansive power of the water in freezing acts in all directions from the center to the circumference, and whatever was on the bottom of the lake has been thus carried to the shore, and this has been going on from year to year, from century to century, forming the embankments which have caused so much wonder.
