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1098 MODDE ET AL. s, the average at 19 floodplain transects as deter- mined by Flo Engineering [1996]). Larval pres- ence in the river was compared with both existing flows (i.e., regulated output from Flaming Gorge Dam) and unregulated flows (those that would have occurred during the same time without the dam). Regulated flows were determined from U.S. Geological Survey gauge records for the Green River at Jensen, Utah, and unregulated flows were estimated for the same site from inflow records into upstream reservoirs (Flaming Gorge and Fon- tanelle reservoirs) plus tributary inflows (Tom Ryan, personal communication, U.S. Bureau of Reclamation). Fish community composition and abundance.- The total numbers and biomasses of fishes in Old Charley Wash were determined in autumn 1995 and summer 1996. The census was done by drain- ing the wetland and concentrating fish in the outlet structure, where they were collected with seines. A 6.4-mm screen on the outlet drain prevented the escape of fish from the wetland. Draining occurred from 25 September to 12 October 1995 and from 17 July to 18 August 1996. All larger fishes (i.e., those estimated to be age 1 or older) were sepa- rated and weighed by species. The following lengths were used to demarcate age-1 or older fish: common carp Cyprinus carpio, 150 mm; green sun- fish Lepomis cyanellus, 75 mm; black bullhead Ameiurus melas, 100 mm; channel catfish Ictalurus punctatus, 150 mm; black crappie Pomoxis nigro- maculatus, 150 mm. Estimates of length frequency and individual weights were determined by sub- sampling. The total weights of smaller fishes were estimated by subsampling the aggregate sample after removal of the larger fish. The total biomass of each smaller species (or life stage) was deter- mined by multiplying the percent weight of the subsample by the total weight of the aggregate sample. Average individual weights in small-fish subsamples were divided into total weight per spe- cies to estimate totals. All fish not individually measured and weighed were visually scanned to detect the presence of rare species. Results Water Quality and Zooplankton Discharge inundated Old Charley Wash (>396 m3/s) between 21 May and 2 July 1995 (48 d; peak daily average flow of 527 m3/s on 8 June) and between 8 May and 14 June 1996 (38 d; peak daily average flow of 623 m3/s on 20 May). Water tem- peratures were warmer both years in the wetland than in the main channel through spring and sum- mer (Figure 2), Maximum surface temperatures recorded in the wetland were 26.2°C (15 July) and 26.6°C (10 July) in 1995 and 1996, respectively. Subsurface dissolved oxygen was not below 4.0 mg/L in 1995 (Figure 2). Depth differences in dis- solved oxygen occurred in 1996, particularly in late June and early July after aquatic macrophytes became abundant. Nonetheless, dissolved oxygen remained above 2.0 mg/L into July. The maximum depth in Old Charley Wash exceeded 2.0 m when the wetland was connected to the river and de- clined to approximately 1 m by midsummer (Fig- ure 2). Although spring runoff patterns differed be- tween years (Figure 3), with peak flows in 1995 occurring nearly 3 weeks later than in 1996, zoo- plankton abundance peaked near the third week of June in each year. Zooplankton samples consisted primarily of cladocerans and copepods. Peak zoo- plankton densities occurred either shortly before (1995) or after (1996) riverine flood waters reced- ed from the wetland (Figure 3). The peak numbers of zooplankton per liter were 54.3 in 1995 and 42.8 in 1996. Larval Fish Presence and Floodplain Access Larval razorback suckers were collected each year between 1993 and 1996 in the study area (Ta- ble 1). They did not have access to most floodplain wetlands (i.e., river discharge > 575 m3/s) be- tween 1993 and 1996, when discharge was regu- lated by Flaming Gorge Dam (Figure 4). In the unregulated scenario, flows were sufficient to al- low access by larvae to the average floodplain wet- land in the Ouray area of the middle Green River during 3 out of 4 years (Table 1; Figure 4). Fish Community Composition and Abundance Comparable numbers of species were collected both years after wetland draining (Table 2). Sand shiners and speckled dace were identified only in 1996, but they were probably present and cate- gorized as miscellaneous minnows in 1995. Total biomass collected during draining was 126.7 kg/ ha and 71.4 kg/ha in 1995 and 1996, respectively. Species composition in both years was dominated by nonnative fishes, particularly common carp and fathead minnow, which accounted for 91.2% of the weight and 60.6% of the fish collected, re- spectively. Other species constituting more than 1% of either biomass or numbers included green sunfish, black bullhead, channel catfish, and red shiners.