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1 1 The relationships between timing and duration of reproduction and stream flow and water temperatures that we found for 1997 to 1999 were similar to those found by Muth et al. (1998) from 1992 to 1996. Our analyses with relatively sparse data suggested that razorback sucker spawning in the middle Green River occurred from early May to early June when flow levels were increasing or at their peak and when water temperatures were in the 10 to 17°C range. Spawning was earlier in the lower Green River, from late Mazch to early June, and over a longer period, than in the middle Green River perhaps because the river warms earlier at that lower elevation. Flow levels during razorback sucker spawning in the lower Green River were relatively low compared to the middle Green River because of earlier reproduction, but occurred at a similar 6 to 15°C temperature range. This suggested rising water temperature or absolute temperature level maybe amore important environmental cue for spawning than flow level. Changes in historical stream flow and temperature patterns may affect not only spawning periodicity but also recovery potential of endangered razorback sucker. Recommendations for operation of Flaming Gorge Dam in the upper Green River system included increasing the frequency and duration of spring flows to inundate flood plains (Muth et al. 2000). Flood plain inundation may create relatively food-rich and warm areas for larvae ofspring-spawning razorback suckers, which may enhance their recruitment success. A key element of that flow management scenazio is to time releases to provide habitat when larvae are present (e.g., post- emergence}. Based on limited capture data, larvae were present in the lower Green River prior to or during most of the high flow periods from 1997 to 1999. Relatively early spawning in that azea would allow larvae to incubate and emerge about the time that flows were peaking. In contrast, capture dates of the few larvae available from the middle Green River in 1997 and 1998 coincided only with the latter part of spring peak flows, or with declining flow levels. This was the case for 27