Monthly mean bottom temperatures for the two areas were similar, 

 reaching peaks of about 30° C. in June I960 and 28° C. during June -September 

 1961. (See accompanying graph.) Lows of about 12° C. were recorded during 

 December I960 to February 1961 and of 10° C. in January 1962. This latter 

 measurement was recorded as a cold front passed during the period January 

 11-15. Sustained low temperature led to the formation of a 2-inch cover of 

 ice on portions of Clear Lake and Offatts Bayou. 



Monthly mean bottom salinity in Clear Lake, due to a direct source 

 of fresh water through Clear Creek and a narrow elongated connection restrict- 

 ing the intrusion of more saline waters from Galveston Bay, was continually 

 lower than that recorded for Offatts Bayou, which lacks any sizable source of 

 fresh water and has a broad connection with West Bay. The difference ranged 

 from about 7%o to as much as 23%o during the study period. Heavy rainfall dur- 

 ing the months of June and July resulted in a generally lower midsunnmer sa- 

 linity than was noted for a similar period in I960, especially in Offatts Bayou 

 where the bottom salinity, which averaged between 28%o and 29%o for July of 

 I960, averaged less than 1 5%o in July 1961. The midsummer drop in salinity 

 is usually more clearly defined in Clear Lake than in Offatts Bayou and seems 

 to occur with predictable frequency. Thus the average spring and fall salinity 

 in Clear Lake ranges from biob to 87cio while the summer salinity ranges from 

 3%o to 57oo. From the last week of June through the second week of July in 1961, 

 the bottom salinity averaged less than l%o. In September 1961, the passage of 

 Hurricane Carla caused a second drop in salinity. 



Forty -five species of fish and invertebrates were taken by trawl- 

 ing in Clear Creek, and fifty -five in Offatts Bayou. The larger number of 

 species taken in Offatts Bayou is characteristic of the more marine portions 

 of Texas estuaries. However, the average number of organisms per trawl haul 



Clear Lake (256 trawl hauls) 



Offatts Bayou (433 trawl hauls) 



24, 626 



49 



