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<br />Eckman dredge samples from the Colorado River in the Grand Junction area <br /> <br />revealed a substrate of sand and muck. The only larva collected were Chironomidae <br /> <br />(blood worms) although adults of Baetis (mayflies) and Isogenus (stonefly) were <br /> <br />observed emerging from the River. Larva of these two genera were collected <br /> <br />elsewhere only on rubble covered substrates indicating this type of environment <br /> <br />is present in the lower .stretches of the Colorado River. <br /> <br />A.lgal growths covered most of the riffle. areas examined above Rifle, Colorado. <br /> <br /> <br />Lush, thick strands. of Filamentons algae, Cladoporha sp. and Mouqaotia sp. up to <br /> <br /> <br />a foot in le.ngth were observed from October, 1973 through February, 1974 <br /> <br /> <br />apparently surviving and functioning duri.ng the coldest period of the year. <br /> <br />The muck deposits on the river bottom were also examined for algal growth. <br /> <br />The thin brown layer of matter at the water-sediment interface was found to be <br /> <br /> <br />heavily colonized by diatoms. Microscopic strands of unidentified origin and <br /> <br /> <br />composition held the diatoms and particulate material in a mat that could be <br /> <br /> <br />lifted off the river bottom revealing the black muck underneath. <br /> <br />List of Diatoms Colonizing the Sediment Surface <br /> <br /> 1. Nitzchia acicularis 8. Nitzchia pelea <br /> 2. Caloneis 9. Gyrosigma <br /> 3. Diatoma 10. Oscillatoria <br /> 4. EUglena 11. Navicula graciloides <br /> 5. Cocconeis 12. Cymbella <br /> 6. Scenedrus quadricanda 13. Lyngbya <br /> 7. Synedra <br />Of these N. palea is a polluted water species. <br /> <br />-16- <br />