Biological Survey — Genesee River 67 



A white disc 10 cm. in diameter lowered into the water at noon, 

 August 26, 1926, disappeared from view 16 feet below the surface. 

 On account of its shallowness and the low transparency of the 

 water, Silver lake shows no stratification in its plankton life. 

 Rooted plants occur only in the shallow water near the shore and 

 at the ends of the lake; none were observed below the 15-foot 

 depth. 



Vegetation of Silver Lake.* — The largest beds of water weeds 

 occur at the south end of the lake and at the north end, including 

 the inlet and outlet streams. The vegetation along the east and 

 west shores of the lake is very sparse except for a few beds of 

 'Sveeds" in the small coves along the west shore. The most com- 

 mon plant in Silver lake is eelgrass {VaUisneria americana) . 

 Several species of pondweeds {Potamogefon) are also abundant 

 and form the bulk of the vegetation in many places. Stonewort 

 {Chara sp.) is very common and sometimes occurs in pure stands 

 over extensive areas. The map (Fig. 9) indicates the character 

 of bottom in the vegetation zone and shows the location of the 

 most extensive beds of weeds found in Silver lake. 



Plankton. — Quantitative estimations of net plankton and nanno- 

 ])lankton were made at three depths in Silver lake, namely, 1-10, 

 10-20, and 20-30 foot strata. The usual methods of obtaining 

 and estimating them were employed. 



In the net plankton no striking differences were noted in the 

 plants of the different depths (Table 6). The most abundant 

 plants found were diatoms, AsterioneUa sp. predominating. The 

 blue-green algae were well represented. A "bloom" composed of 

 RivuJaria, Aiiahaena, and Aplumocapsa almost completely covered 

 the surface of the lake during the latter part of August. The 

 number of animals found in the net plankton was low. In the 

 case of protozoa, with the exce])tion of Ceratium, the figures prob- 

 ably do not represent a true value because it was not possible to 

 make these counts at the time the plants were counted. The 

 enumeration of undetermined animals, practically all protozoa, 

 at the time shows that there were large numbers of individuals 

 present. By comparison with the net plankton the nannoplankton 

 values are low. 



* For a complete list of the larmier ]ilaiits orowino- in Silver lake and 

 Conesns lake, see Appendix \\\. 



