670 U. S. BUREAU OF FISHERIES 
just above Minneapolis to just above Winona. Winona is about 110 miles below 
St. Paul. 
The sampling stations on the Mississippi River were so distributed that data 
were obtained (a) before any sewage had entered, (0) after all the Minneapolis 
sewage had entered, (c) again after all the St. Paul sewage had entered, and 
one tributary, the Minnesota River, had entered the Mississippi R.ver, (d) after 
the South St. Paul sewage has been added, and (e) at various distances below 
these points, where most of the sewage is added. In order to obtain com- 
parative data from unpolluted streams, samples were taken from the Minnesota, 
St. Croix, Cannon, and Chippewa Rivers also. 
To give you some idea of conditions in the Mississippi River below the Twin 
Cities, I might mention the fact that all the domestic sewage and trade waste 
from the cities (joint population approximately 650,000) is dumped into the 
river without having been treated previously. In addition to this, some 7 or 8 
miles below St. Paul are the packing plants of Swift and Armour, so situated 
that all of their sewage goes into the river. The packing interests, of course, 
claim that they utilize everything except the squeal. If that is true, the squeal 
must have some extremely obnoxious qualities. 
Within the Minneapolis area conditions are aggravated further by the Ford 
power dam, situated just below the city. This dam causes the settling out of 
most of the solid materials in the Minneapolis sewage. The city engineer 
claims that there already exists a 12-foot layer of sludge behind the dam, and 
that this deposit is increasing at the rate of 12 inches a year. 
As the time is rather limited, I shall not attempt to give a detailed discussion 
of the survey but shall confine myself to a brief statement. 
The determinations of dissolved oxygen made by Mr. Crohurst, who is in 
charge of the sanitary survey that is being made by the United States Public 
Health Service, show that for the month of August the amount of dissolved 
oxygen just below Minneapolis was 0.67 parts per million; just below St. Paul 
it was 0.87 parts per million; about 3 miles below the packing plants of Swift 
and Armour it was 0.51 parts per million; and at Hastings, about 36 miles 
below St. Paul, it was 0.39 parts per million. At Red Wing, at the head of 
Lake Pepin, the average for the month was 2.25 parts per million; but even 
here there were 11 days during the month when the dissolved oxygen was less 
than 2 parts per million. In the Mississippi River above Minneapelis the 
average for the month was 6.59 parts per million. At the lower end of Lake 
Pepin it was 5.87 parts per million, and at Winona 599 parts per million. For 
the tributaries—the Minnesota, St. Croix, Cannon, and Chippewa Rivers—the 
amounts of dissolved oxygen were 5.70, 7.10, 7.48, and 6.26 parts per million, 
respectively. 
The bottom fauna of the Mississippi River above Minneapolis is dominated 
by clean-water species: May-fly nymphs, caddis-fly larve, planaria, and the 
larve of Simulium. In the metropolitan area and below it, as far down the 
river as Hastings, the bottom fauna is dominated by sludge worms (Tubificide). 
In one instance the number of sludge worms per square yard exceeded 300.000. 
Red Wing marks a transition in the condition of the Mississippi River. This 
is shown by the decrease in the number of siudge worms and the increase in 
Mollusca and leeches; also by the presence of large numbers of Hyalella and 
a few specimens of Asellus in August and a few dragon-fly nymphs and caddis- 
fly larve in September. 
At Winona, May-fly nymphs are found again along the shore. This may be 
taken as a sign that the river has been purified sufficiently to support the life 
of clean-water species. 
The data on dissolved oxygen and the bottom fauna show that the upper 
Mississippi River is grossly polluted from within the metropolitan area and 
down to the head of Lake Pepin. Lake Pepin acts as a settling basin. At 
the lower end of the lake and at Winona the waters of the river are greatly 
improved. Such being the case and knowing that the tributaries are not pol- 
luted, the conclusion that the pollution of the Mississippi River is due to the 
sewage from the Twin Cities seems warranted. 
The study of the plankton shows apparently nothing, as far as pollution is 
concerned. Variations in the amount and character of the plankton occur, but 
these variations are not sufficient to warrant the conclusions that they are due 
to pollution; they probably are seasonal variations. 
Game fish and other small fish were abundant in the Mississippi River 
above Minneapolis and in the tributaries—the Minnesota and the St. Croix 
