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on March 2, 1988 at a discharge of 340 cfs (9.6 cros). On Apri16, just after ice-out, an average daily discharge of 1,450 cfs (41.1 cros) resulted in the same stage elevation of 92.14 feet. Ice Conditions Surface ice covered the Yampa River from December through early March in both winters investigated. Ice cover in large streams, like the Yampa River, is normally in floatation (Rantz 1982). As stage increases or ice thickens, increased upward force by the water causes tension, or coastal, cracks in the ice, usually near the banks. The ice Iloats to a position of equilibrium, and water fills the tension cracks and refreezes to form a solid ice cover. This same phenomenon occurs with a drop in stage, where weight of the unsupported ice causes stress cracks along the banks and the ice falls to an equilibrium position with the water. Under extremely cold conditions, heavy surface ice in contact with the stream may resist this state of equilibrium, causing flow conditions to more closely resemble a closed conduit. In mid-February, small increases in discharge (197 to 229 cfs; 5.6 to 6.5 cros) of the Yampa River were not sufficient to raise the level of the ice. The cross sectional area remained fixed, like a closed conduit, resulting in an increase in water velocity. Just as the process of ice formation throughout winter effectively increased stage at a given discharge on the Yampa River, spring breakup had the opposite effect. In cross sectional measurements taken March 3 and 15, 1988, a 10 cfs decrease in discharge resulted in a stage reduction of 0.4 feet (12.2 cm). This was caused by warm air temperatures in March, and loss of shoreline ice at anchor points. This resulted in an increase in water flowing along the river's edge, loss of the damming effect of the shore ice, and reduction of stage at a given flow. Spring breakup was a critical period for fish in the Yampa River, as low-velocity habitats became invaded by flowing water. Bed changes also occurred as sediment moved with shifting currents. The Yampa River fish were noticeably more active during spring breakup, also described by Wick and Hawkins (1989) as a violent event. Large slabs of ice tilted and scraped along the river bottom, leaving dramatic changes in the channel bed, such that a backwater at RM 95.7, was nearly tilled with large amounts of gravel. Three radiotagged Colorado squawfish that had occupied this backwater throughout winter, moved to another downstream location. In contrast, radiotagged fish using an embayment at RM 81.1 remained in place, as very little ice was deposited and no changes were seen in the embayment during breakup. Movement And Habitat Of Radiotagged Adults Ten adult Colorado squawfish were radiotagged in each of two subsequent winters in the Green and Yampa rivers, to monitor movement, local activity, habitat use, and response to changing 20