LIMNOLOGICAL OBSERVATIONS IN THE UPPER MISSIS- 
SIPPI, 1921. 
& 
By P. S. GALTSOFF, 
Naturalist, U. 8. Bureau of Fisheries Steamer Albatross. 
& 
CONTENTS. 
Page. 
Introduction 347 
Method of investigation 351 
Schedule of localities 351 
Boat and equipment 353 
Instruments 353 
Pump 354 
Determination of plankton 354 
Stations 355 
Physiography 357 
The river 357 
Lake Pepin 359 
Lake St. Croix 360 
Lake Keokuk 360 
Stages 362 
Velocity of current 366 
Discharge 369 
Flow of sediment 370 
Chemical constituents of water 371 
Transparency of water 371 
Temperature of water 373 
Page. 
Plankton and detritus 375 
Volume 375 
Horizontal distribution in river 379 
Vertical distribution in river 379 
Lake Keokuk 380 
Lake Pepin 382 
Lake St. Croix 384 
Pump and net collections 385 
Distribution of Copepoda and Cladocera 387 
The river 387 
Lake Keokuk 389 
Lake Pepin 394 
Composition of the plankton 396 
The river 403 
Lakes 406 
Tributaries 410 
Discussion and conclusion 411 
Potamoplankton 411 
Plankton and the fisheries 415 
Summary 420 
Bibliography 434 
& 
INTRODUCTION. 
The present paper deals with the results of the hydrobiological investigation 
of the section of the upper Mississippi between Hastings, Minn., and Alexandria, 
Mo., which is about 465 miles long if measured along the steamboat channel. At 
the extreme ends of this section the river forms two lakes — Lake Pepin and Lake 
Keokuk (fig. 3, p. 352). Lake Pepin, located 28 miles below Hastings, is a natural 
lake about 25 miles long and from 1 to 3 miles wide. Lake Keokuk is a recently- 
formed basin that extends northward above the Keokuk Dam for about 60 miles. 
Between these two lakes, about 130 miles above the foot of Keokuk Lake and 240 
miles below the foot of Lake Pepin, the river flows through the so-called Rock 
Island Rapids. The bed of the river here forms a series of steps causing rapids with 
a total fall of 21 feet in 16 miles. The character of the river above and below the 
347 
