Section Page 



18 Dimensions of the Great Lakes 197 



18 Estimated average concentration of dissolved chemical 



constituents in the Great Lakes prior to 1900 198 



18 Estimated population in Great Lakes Basin, 1900-1960 ... 203 



18 Summary of fish species decline in the Great Lakes by 



year, lake, and current commercial production 205 



18 Estimated average concentrations of dissolved chemical 

 constituents in the Great Lakes in 1925 with percentage 

 change after 1900 in parentheses 206 



18 Fish-species introductions in the Great Lakes by year 

 and lake, first year of commercial significance, and 

 current production 208 



18 Fish species in the Great Lakes that have experienced 

 severe declines, lake affected, and suspected cause of 

 decline 209 



18 Estimated average concentrations of dissolved chemical 

 constituents in the Great Lakes in 1950 with percentage 

 change since 1925 in parentheses 210 



18 Estimated average concentrations of dissolved chemical 

 constituents in the Great Lakes in 1970 with percentage 

 change since 1950 in parentheses 214 



XI 



