the average there was less decomposing organic matter, as shown by albuminoid 

 anmonia, than in the Island Section. In most of the sar.iples the oxygen con- 

 tent was in excess of 90 per cent of saturation, and in only a few samples 

 was it less than 30 per cent of saturation. Doubtless the nitrogen content 

 of the river water has been increased as a result of pollution, but probably 

 the increase has been too small to have an appreciable effect on the oxygen 

 content of the water. It may be concluded that pollution in Detroit River 

 has had no harmful chemical effect on the water of Western Lake Erie. 



The relative positions of the different sections ^^^.th respect to inten- 

 sity of pollution as indicated by the chemical data, particularly albuminoid 

 ammonia, were: (1) Maumee Bayj (2) River Raisin: (3) Portage River; (U) 

 Island; (5) Detroit River. In the lower parts of Maumee an.] Raisin Rivers 

 and sometimes in small areas in the lake near the mouths of these rivers, 

 pollution was sufficiently intense to make the chemical conditions harmful to 

 aquatic organisms which would normally inhabit such areas. In the Portage 

 River, Island and Detroit River Sections there was no evidence of pollution 

 of sufficient intensity to cause harmful chemical conditions. 



The result? and conclusions reviewed above refer to the period when the 

 lake is free of ice. Determinations of oxygen, carbon dioxide, and pH, made 

 under the ice near the west shore when the period of ice-closure was about 

 three-fourths completed, indicate that cherai cal conditions there were little, 

 if any, less favorable than those prevailing during the summer. 



The available evidence, both direct and indirect, indicates that poisonous 

 substances are not present in the lake in concentrations sufficient to affect 

 aquatic organisms harmfully. 



The final conclusion to be drawn from the chemical data is that pollution 

 has had both harmful and helpful effects en chemical conditions in Western 

 Lake Erie. The harmful effect has beenthe marked reduction in oxygen content 

 of water discharged into the lake from Maumee and Raisin Rivers. The helpful 

 effect has been the addition to the lake water of large quantities of nutri- 

 tive materials, which probably have made possible a great increase in the 

 abundance of plankton organisms. It is probable that the harmful effect has 

 been offset, largely if not entirely, by the helpful effect. 



Phytoplankton 



A qualitative study of the quantitative samples showed the presence of 

 80 genera and 1^0 species of algae. The list is conposed principally of rep- 

 resentatives of the Chlorophyceae, Diatomeae, and Myxophyceae. Representa- 

 tives of other classes are relatively few in number. 



The horizontal distribution o f the phytoplankton was not uniform in the 

 Island Section. There was little evidence that some stations had consistently 



