Htkeym Pol^utiojst 4:7 



where they became sick from sewage and could be picked up easily 

 with a dip net. The following morning a 3 pound carp, 2 hooked 

 dace {Semotilus atromaculatus) , and an orange spotted sunfish 

 were obtained in this way. " In August 1912, * * * below the 

 dam * * * we got a greater variety of species in shallow water 

 along shore near the mouths of small tributaries. * * * A com- 

 parison * * * makes it probable that most of the specimens 

 taken from the river here were immigrants from the creeks." 



At Ottawa in August fish were much more abundant. " From a 

 comparison * * * it is plain that Fox river water was greatly 

 preferred by fishes at this place and it seems likely indeed that most 

 of the specimens taken at this point had come into the [Illinois] 

 river from the Fox." At Starved Rock as a result of extensive 

 collecting " it seems that the fishes taken here represented the nor- 

 mal river stock at this place with practically no immediate admixture 

 from small tributary streams." " At Hennepin we found commer- 

 cial fishing in progress in both the river and the adjacent lakes. 

 This was the first station at which the life of the river may be said 

 to have found virtually normal conditions." 



While Forbes and Richardson found as shown above that the 

 large majority of fishes were driven away by pollution, or if carried 

 in by chance were unable to sustain themselves in the polluted 

 sections of the Illinois river, there was at least one exception to 

 the rule; indeed, so far as their experience went, only a single 

 species of fish was an exception to it. The common shiner (Notropis 

 atherinoides) was often collected in numbers when no other fishes 

 were found; as a result of their experience, these authors say that 

 this abundant lake and river minnow is " unusually tolerant of 

 polluted waters." 



Minnow Test 



Chemical and bacteriological methods have rarely been employed 

 in stream examination by men associated with work on fish prob- 

 lems. They have, however, used fishes as an index of stream con- 

 ditions, and have commonly employed the so-called minnow tests as 

 a basis for deciding whether, for instance, the pollution in a given 

 stream reaches the extent specified in the Conservation Law and 

 consequently whether the discharge of the wastes should be pro- 

 hibited. The test probably owes its popularity to the ease with which 

 it may be applied and, when the conditions of its use are safe- 

 guarded, one must recognize that it is a reasonably satisfactory 



