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meter in backwater habitats. Obvi ously, the backwater habitats were more productive than the main channel in chironomid production. Another study evaluated macroinvertebrate densities in the main channel, side (ephemeral) channel, and two types of backwater habitats in the middle Green River south of Vernal, Utah. The numbers of chironomids in the main channel ranged between 3,500 and 4,200 organisms per square meter, the range for the side (ephemeral) channel was between 2,300 and 8,100 organisms per square meter, in one backwater (bas i ca 11 y a ri vers i de pond) the range of ch i ronomi ds was between 9,000 and 23,000, and in the other backwater, the range was between 22,800 and 31,100 organisms per square meter (Table 2; Wolz and Shiozawa 1995). Three baseline studies were conducted of wetland habitat sites in bottomlands of rivers in the upper basin. The wetland at Escalante Ranch along the middle Green River, upstream from Jensen, Utah, produced a mean of 17 chironomids per square meter in the main channel, 17 organisms per square meter in a backwater, and 31 organisms per square meter for an open water wetland (Table 2; Cooper and Severn 1994a). At another wetland site, Cooper and Severn (1993) reported a mean of 11 chironomids per square meter in the main channel of the Colorado River immediate upstream from Moab, Utah. They reported a mean of 4 chironomids per square meter in a backwater site and a mean of 11 organisms per square meter for an open water wetland. The Gunnison River at the Escalante State Wildlife Area, about five miles downstream from Delta, Colorado, contained a mean of about 496 chironomids per square meter, a backwater contained 1,141 organisms per square meter, and an open water wetland contained 1,092 organisms per square meter (Table 2; Cooper and Severn 1994b). The mean number of benthic chironomids per square meter in a flooded bottomland (Old Charlie Wash) was 33 (Table 2; Cooper and Severn 1994c). Cooper and Severn (1994c) reported a mean number of chironomids for a backwater at 21 organisms per square meter and 10 from the channel of the middle Green River on the Ouray National Wildlife Refuge. Microcrustaceans that form zooplankton communities are also found in the substrate of aquatic habitats. Mabey and Sh i ozawa (1993) reported between 1,000 and 6,300 benth i c microcrustaceans (Cladocera, Copepoda, and Cyclopoida) per square meter in the ma in channel of the mi ddl e Green Ri ver through the Ouray Nat i ona 1 Wil dl ife Refuge, between 4,900 and 6,000 organisms per square meter for a backwater, 23,000 per square meter at Intersection Wash (a large backwater), and between 8,600 and 263,000 per square meter in Old Charlie Wash (basically an open water wetland or riverside pond). VIII. RELATION OF FOOD TO LARVAL FISH SURVIVAL Larval fish must initiate feeding during the "critical period" before they reach "a point of no return II (Li and Mathias 1982; Miller et al. 1988) or high mortality occurs from starvation if competition is high (May 1974). Adequate densities of zooplankton prey are important to the growth and survival of larval fish (Welker et al. 1994). At low prey densities, Welker et al. state that intra- and interspecific competition may reduce the growth and survival of larval fish. The timing, extent, and duration of flooding greatly influences fish species that use floodplain habitats and these factors may exert a moderate to strong control in year-class strength of some fishes (Lambou 1963; Baker and Killgore 1994). The year-cl ass strength of fi sheri es is often determi ned by envi ronmenta 1 conditions (i.e., critical period) such as suitable water temperature as well as 8