organisms were ollgochsietes (worms) and insects. Most of the latter were 

 immature stages of the orders Diptera (flies) and Trichoptera (caddisflies) 



The river was divided into four major environments. 



The upper reach of the river (above mile 229) was characterized 

 by animals which inhabit clean, fast-flowing water, such as caddishflies, 

 mayflies, stoneflies, true flies, and oligochaetes . This reach contained 

 the greatest average number of organisms, average ntunbers of genera, and 

 average volvmes of organisms per square foot of sanipled area. 



The lower reach (mile 18.8 to mouth of river) was the next most 

 productive area. This reach contained primarily clams, amphipods, oligo- 

 chaetes and midge larvsie. 



The two middle reaches were relatively unproductive. Most of 

 the organisms collected were oligochaetes, midge larvae, and clams. 



One large seasonal variation in animal abvuadance was noted. 

 Production of bottom organisms steadily increased from July through Novem- 

 ber i960 in the reach above mile 229- A sharp drop in numbers was noted 

 in December I96O and Jan\iary I96I. This drop in numbers followed very 

 high river flows in late November. 



Recommendations 



1. Knowledge of the taxonomy and life histories of many of 

 the orgsuaisms collected during the survey should be expanded. 



2. A more complete evaluation sho\ild be made of the data col- 

 lected during the Sacramento River Water Pollution S\irvey in order to 

 establish the relationships between biological populations and their 

 environments. 



-TU- 



