MAJOR VEGETATION OF LAKE OKOBOJI 
93 
areas represent portions of the lake bottom having large plants, 
other than Ceratophyllum, and including Chara beds (Fig, 12). 
Since Okoboji is much the deepest of this group of lakes and 
has large areas of considerable depth one is surprised to learn the 
extent of the weed-beds in its waters. According to this survey 
about eleven hundred acres of lake bottom are occupied by larger 
plants. The total area of the lake is approximately 3700 acres 
which means that nearly thirty per cent of its area was underlaid 
with plants in 1919. This does not mean of course that they 
showed at the surface over that proportion of the lake; in most 
places they were entirely out of surface view. 
In discussing these findings it should be borne in mind that the 
extent and character of these weed-beds vary somewhat from 
year to year. Modifications of the season, particularly the spring 
and early summer, would likely alter the relative proportion of the 
various species. Obviously changes in the lake level, from year 
to year, would markedly influence their lateral distribution. With 
lower water level the deeper species could grow out farther into 
the lake. Since these forms are very sensitive to depth a depres- 
sion of a foot or two in lake-level would permit a marked en- 
croachment under the open waters of bays where the substratum 
is suitable for these species. All attempts to artificially modify 
the level of the water should take into account the certain influ- 
ence such changes would have upon the vegetation of the lakes. 
Lower water would mean not only considerable extensions of 
weed-beds, but would bring to the surface areas of weeds not 
suspected at higher levels. 
The following list includes the species that are most commonly 
found in Lake Okoboji : 
Bidens Beckii Torr. Potamogeton praelongus Wulf. 
Ceratophyllum demersum L. Potamogeton pusillus L. 
Elodea ioensis Wylie. Potamogeton Richardsonii (Benn.) 
Heteranthera dubia (Jacq.) MacM. Ryd. 
Myriophyllum spicatum L. Potamogeton zosterifoliiis Schum. 
Naias flexilis (Willd.) R. & S. Ranunculus circinatus. Sibth. 
Potamogeton amplifolius Tuck. Scirpus validus Vahl, 
Potamogeton natans L. Vallisneria spiralis L. 
Potamogeton prectinatus L. Zannichellia palustris L. 
Other species of aquatic plants are occasionally encountered 
but the above named forms constitute the chief formations of 
the lake. Forms like the duckweeds are frequent migrants from 
ponds having outlet into the lake but do not thrive in the open 
