Biological Survey — Erie-Niagara Watershed 



00 



this set of measurements, which lasted 12 hours, being 0.44 ft/sec, 

 occuring" at 4 a.m. on the ^Jlst. 



Tlie velocities encountered during the fourth cruise were not 

 as large and hence the high currents reported by the fishermen 

 who claim that their nets and gear are damaged thereby must still 

 remain a matter of hearsay, although it is probable that they do 

 not exist. 



In the complete report, to be published elsewhere, it is shown 

 that the currents of Lake Erie cannot be due to the "normal flow'' 

 of the water from the western to the eastern end ; and that these 

 currents must be brought about by winds, barometric pressure, 

 the distribution of density, or combinations of these factors. In 

 this fuller discussion, a theory to account for the movement of the 

 cold water noted in the pages above is advanced and fully dis- 

 cussed. The suggestion is offered that data supplied by the weather 

 bureaus of the lake cities may ultimately permit the location of 

 this cold w^ater to be forcasted day by day. Since several of the 

 commercial species of fish follow this cold water closely, the 

 economic value of such forecasting is evident. 



Transparency. — The transparency of Lake Erie as a whole is 

 low. The maximum reading of the Secchi disk w^as only 10.5 meters 

 with a minimum reading of 2 m. The average was between 5 

 and 6 meters. 



The plotted distribution of the data showed no particular geo- 

 graphical effect, the near shore stations being about as high in 

 value as the off shore. The roughness of the sea decreased the 

 transparency and the angle of the sun had some effect for the 

 highest values occurred on sunny quiet days within a few hours 

 of noon. The abundance of living organisms probably played the 

 most important part in varying the transparency, and mean value 

 (5-6m.) which we found in the eastern part of the lake is about 

 what might be expected in a ''green" sea. Harvey* gives the 

 transparency average for the Deutschland Expedition's tests in 

 ''green" sea w^ater as 9 m. 



* Harvey, H. 

 p. 157, 1928. 



W. Biological Chemistry and Phvsics of Sea Water, table 43. 



