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.;,:;. .~;; On the whole there appeared to be abundant ni trogen and phosphorus , as well as other nutri ents ava il ab 1 e for algal growth. However, with the exception of the s.ample collected at Masters during October, the addition of nutrient to the water stimulated algal growth. The sample that showed no additional growth 'when more nutrient was added would indicate that luxury amounts of nutrient were available. This is what had been expected from all samples prior to performing the algal assays. However, the results of the assays would indicate that nutrients could be limiting at times. Even if nutrient limitation SReuld occur, it is obvious that a large algal standing crop would develop first. The algal standing crop would be likely to be maintained at a high level. Algal growths in excess of the maxima obtained during these assays have been observed in several mainstem reservoirs on the North Platte River in southerli Wyomihg(USGS, 1976). .. l'heseoccurduring what appears to be an annual bloom of the blue-green alga Aphanizomenon sp. during late August or early September. These North Platte Reservoirs appear to exhibit a temperature regime similar to that obtained in the previously described temperature simulation; however, the maximum temperature is somewhat lower than that projected for.the Narrows Unit. The North Platte Reservoirs experienced some oxygen depletion in the deeper waters during 1975, but there was no evidence of an oxygen,deficit (USGS, 1976). These reservoirs are extensively used for recreation. Concurrent with the collection of water samples during August, artificial substrate samplers were placed in the river at each of the two above described stations. These consisted of bark samplers for invertebrate sampling and microscope slides for algal sampling. Organisms collected were identified and standard diversity indices (SoI) were calculated, At !:>oth sta:tJons the humberpfili.v~r:t,ebrates collected was low. The samplers on several occasions were observed to be buried in the bed material,which consisted primarily of sand and gravel. The stream bed undOUbtedly limits invertebrate productivity. At the Masters station invertebrates consisted of caddisfly, tendipid, and mayfly larvae. The SOl's calculated from the two samples at this station were 1.9 and 1.5. Only one of the two samplers was recovered at the downstream station. Invertebrates in this sample comprised only caddisfly and tendipid larvae. The SOl on this sample was 1,0. 22 ,. -c-'.' -. ;.-... > -,<-'.:. -~,' . -~, .;....-.