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We make this estimate using the 1993 daily hydrographs for the Green River presented in Figure 4 and the first author's visit to the study area on 20 May 1993 when flooding was occurring through the Fremont cottonwood forests in the Leota Bottom area. On this date the Green River was flowing at approximately 17,000 to 19,000 cfs. According to the refuge assistant manager Dan Schaad the Green River had not flooded in many years, and using the data presented in Figure 3 it can be seen that the area has apparently not flooded since 1986. Large scale flooding did occur in the mid-1980's. Based upon the maximum May and June flow data presented in Figure 3, overbank flows (>17,000 cfs) are estimated to occur .at a frequency of once every 1.45 years for the period 1946 to 1963, and once every 3.3 years for the period 1964 to 1993. Of the 9 years in which overbank flooding has occurred since 1964, 4 of them occurred from 1983 to 1986. Long periods of time with no overbank flooding have occurred, for example from 1987 to 1992. It should be kept in mind that flooding into the basins described above would have occurred on many years prior to river regulation. Once flooded, these basins hold water for long periods of time. We can envision that prior to 1963 flooding during moderate to high water years would fill basins in spring and many basins would retain water through the winter. Flooding the following spring would refill the basins and reconnect the wetland to the river. Sequential flood events (such as occurred annually from 1947 to 1958, with the exception of the low water years 1954 and 1955) would have allowed larval fishes to be washed from the river into these bottoms where they would have grown over the summer, survived the winter (if sufficient water depth was maintained to keep dissolved oxygen content high) and be washed back to the river in a subsequent year. The opportunity for hydrologic connection between the Green River and the immense floodplain marshes in the study area was a characteristic element of the study area. Wetlands such as Leota Bottom and Wyasket Lake are each nearly 1 mile in length! Wyasket Lake provides one of the most valuable wetlands, from an aquatic life perspective, that we have seen. 9