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tubificid worms and dipteran larvae (e. g., Palpomyia and chironomid larvae). Aquatic insects normally abundant in permanent streams, such as mayflies or caddisflies, were not important at either Station 2 or 3 and stoneflies (Ple- coptera) were not collected. f Invertebrates in pools are usually restricted to a few abundant taxa. Many species are limited by the fact that pools in streams exhibit reduced 1 algal production (decreased sunlight), homogeneous silt-covered substrate and the possibility of local oxygen deficits. chironomid larvae and tubificid worms, often abundant in pools, are adapted to this type of habitat. The permanent nature of the beaver ponds at Station 1 resulted in higher densities than the other pool habitats. Chironomids and worms dominated the benthic I density at this station, but amphipods, clams and mayflies were also abundant. An interesting note is the collection of the freshwater sponge, Eunapius fragilis, which is found in a variety of ponds in Colorado with widely varying water quality (Williams 1980). Invertebrate densities in the pools at the 1 lower stations were much lower than Station 1, with amphipods and worms most abundant at Station 2 and chironomid larvae at Station 3. Table 1 also presents number of species and species diversity (D) for the stations on the tributary. Number of taxa generally reflected the available habitat. Many species were found in the pool habitat at Station 1 due to the addition of true standing water (Lentic) water forms not usually found in pools of streams. The number of species in riffle areas was greatest at Station 3, which had more riffle habitat available. The use of the Shannon- Weiner diversity index is encouraged by the EPA (Weber 1973) as a measure of the effects of stress on the macroinvertebrate community. Diversity values from riffle areas were similar at Stations 2 and 3 with values typical of this type of stream. Pools are generally a poorer source of species (Hynes 1970) 1 and this is reflected in the pools at the lower station on the tributary which have very low diversity index values. The higher diversity value at Station 1 1 reflects the addition of Lentic species as noted above. i Foidel Creek A total of 24 species of benthic invertebrates were collected from Foidel Creek with only two found at all four stations (Table 2). Only Station 4 had i ! flowing water and at this station the riffle invertebrates were dominated by Chironomidae Form 1 and the tubificid worm Limnodrilus. Pool invertebrate i -8- I