The River in Glen Canyon. Epiphytic diatoms and other algae colonizing submerged macrophytes and firm substrata has constituted the primary food-base for aquatic consumers in the tailwaters of the Colorado River ecosystem downstream from Glen Canyon Dam prior to 2000. 

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Major Ecological Changes. Since 1996 the extent and variation in daily flow fluctuations resulting from reduced hydropeaking from Glen Canyon Dam and other operation policies have resulted in a marked compositional transition from a near-monoculture of Cladophora to a dense and dynamic assemblage of multiple macrophyte taxa: Chara cf. vulgaris, Potamogeton cf. pectinatus, Zannichellia palustris, Cladophora glomerata, and a dense bed of the aquatic moss Fontinalis hypnoides. ​​​