LIMNOLOGICAL OBSERVATIONS IN THE UPPER MISSISSIPPI. 357 
Table 2. — Stations and number of samples collected during investigation of upper Mississippi River, 1921. 
Location. 
Number 
of 
stations. 
Samples collected. 
Pump. 
Vertical 
plankton 
net. 
Dip net. 
Total. 
Mississippi River (main channel, sloughs, bays, and abandoned channels).. 
52 
143 
19 
3 
165 
Tributaries of the Mississippi 
19 
45 
6 
5 
56 
Lake Keokuk 
51 
167 
53 
17 
237 
Lake Pepin 
49 
161 
40 
14 
215 
Total 
171 
516 
118 
39 
673 
PHYSIOGRAPHY. 
THE RIVER. 
The source of the Mississippi River has long been the subject of controversy. 
Lake Itasca, Minn., has been regarded as the head of this greatest American river, 
hut according to an accurate map of Itasca State Park, issued by the Mississippi 
River Commission about 1910, Little Elk Lake, in northern Minnesota, latitude 47° 
69' N., longitude 95° 13' W., is the real source of the “Father of Waters.” The long 
history of the discovery of the Mississippi is fully described by Chambers (1910). 
The so-called Itasca State Park set aside by the State of Minnesota now covers 35 
square miles of a basin containing the many glacial lakes forming the headwaters of 
the Mississippi. In scientific literature the upper Mississippi is considered rather a 
tributary of the lower Mississippi than a main stream. It drains 173,000 square 
miles, its total length is 1,293 miles, and its discharge into the lower Mississippi varies 
from 25,000 to 550,000 cubic feet per second. Similar data for the Missouri River 
are as follows : The length from the headwaters to the mouth of the Mississippi is 
about 3,000 miles, drainage area 541,000 square miles, and the discharge from 25,000 
to 600,000 cubic feet per second. The annual rainfall over the upper Mississippi 
Basin averages 35.2 inches and over that of the Missouri 20.9 inches. 
In respect to navigation the upper Mississippi can be divided into two sec- 
tions — from the headwaters to St. Paul, head of navigation, 534 miles, and from 
St. Paul to the mouth of the Missouri, 659 miles. Only the latter is navigable by 
steamboats. The present investigation has covered 465 miles of the navigable 
part of the river; that is, about one- third of the total length of the river or about 
three-quarters of its navigable part. In its course the river forms many rapids 
and falls, the following being the principal ones: St. Anthony Falls, above Minnea- 
polis, Minn.; Rock Island Rapids, between Le Claire, Iowa, and Rock Island, 111., 
where the fall of the waters is about 21 feet in 16 miles; and Keokuk Dam, which 
has raised the water level at mean flow below the dam by 35.3 feet above the stan- 
dard low water. The elevations of the water level at various points of the river, 
taken from the Mississippi River Commission charts, are shown in Table 3. 
