162 



BULLETIN OF THE BUREAU OF FISHERIES 



Station 8.- — On August 19 four seine hauls were made at station No. 8. One haul 

 was made on the St. Croix side at the junction of the St. Croix and the Mississippi 

 Rivers. This haul was not very successful because the net rolled; yet it netted the 

 203 fish shown in Table 12, 1 adult red horse, and 1 adult yellow perch. The last 

 two were thrown back and were not recorded in the table. The second haul, made 

 on the Mississippi River side, netted one turtle. The waters of the two rivers have 

 not yet mixed here. A third haul was made in the St. Croix River, about 3^ mile 

 above its mouth. Here aquatic plants were very abundant along the shore and inter- 

 fered seriously with making the haul. The bulk of the fish taken here consisted of 

 yellow perch and black crappies. At least 150 of each were thrown back and were 

 not recorded in the table. The fourth haul was made on the Wisconsin side of the 

 Mississippi River, about 1 mile below the mouth of the St. Croix River. This 

 haul yielded the 211 fish shown in Table 12, besides 1 large red horse, 1 large pumpkin 

 seed, and 5 four-inch yellow perch. It is doubtful if the waters of the two rivers are 

 mixed to any great extent even here. Time did not permit the making of another 

 haul on the Minnesota side of the river. 



Stations 9 and 10. — On August 28 two seine hauls were made in the Cannon River, 

 a short distance below station 10, and one in the Mississippi River, about 1}^ miles 

 above Red Wing (station No. 9). Because of the high water, weeds, and fallen logs, 

 these hauls were not successful. No fish were taken in the Cannon River, and only 

 one common shiner was taken in the Mississippi River. The waters of the Mississippi 

 River were pushing up into the Cannon River. This made the latter so turbid that 

 if any fish were present they could not be seen. When the writer revisited this 

 river about 2 miles farther up its course, the water was clear and a number of small 

 fish were seen. 



The above data show (1) that fish are abundant at stations 1 and 2 on the 

 Mississippi River, at stations 4 and 8 on the Minnesota and St. Croix Rivers, respec- 

 tively, and in the Mississippi River (Wisconsin side) about 1 mile below the mouth 

 of the St. Croix River; (2) that fish are very scarce, if present at all, in the Mississippi 

 River at and between stations 5, 6, and 7, and in the waters of the Mississippi proper 

 (that is, in the Mississippi waters that were not yet mixed with those of the tribu- 

 taries), at or near stations 8 and 9. Commercial fishing above Red Wing did not 

 commence until the latter part of August, and then only around the mouths of tribu- 

 taries. Below St. Paul carp fishing did not begin until about the middle of September, 

 one month after the beginning of the heavy rains. 



DISCUSSION— FISH AND POLLUTION 



It was shown on page 144 that during August (all my seining was done from 

 August 17 to 28) "the dissolved-oxygen content is decidedly less in that section of 

 the Mississippi River which extends from station No. 2, at the beginning of the 

 metropolitan area, to station No. 9, at the head of Lake Pepin (a distance of 

 approximately 64 miles) than it is above or below this section or in the tributary 

 waters," and "at station No. 9 conditions with respect to dissolved oxygen are much 

 better than they are at stations 3, 5, 6, and 7, but are not nearly as good as they 

 are at stations 1, 2, 11, and 14." Again, it was concluded from a study of the 

 bottom fauna (p. 151) and of the phytoplankton and zooplankton (pp. 157 and 159, 



