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Table 4. Summary of overwinter habitat suitability of9 backwaters sampled during winter of 1994-95. CH = chute channel, SC = scour channel, ER = eddy return channel. ' Site # (River Mile) Suitable Habitat Reason Not Suitable Backwater Channel Type Through Winter Reach 1 1 - CH (533.5) Yes :2 - CH (527.1) No Backwater became a flow-through from unknown channel morphology changes Reach 2 3 - SC (511.7) Yes 4 - ER (508.8) No Ice jams caused damming and flow- through 5 - SC (465.6) No Average water depth <0.3 m; caused by collapsing ice lenses 6 - CH (464.7) No Ice jams caused damming and flow- through Average water depth <0.3 m; caused by collapsing ice lenses Reach 3 7 - SC (418.7) Yes 8 - CH (413.7) Yes 9 - SC (405.3) No Average water depth <0.3 m In Reach 2, multiple ice lenses were common on shorelines and backwaters as a result of daily fluctuations in water levels from dam operations and diel air temperatures. Ice lenses usually formed during cold nights along quiet shorelines and calm backwaters. Fluctuating water levels and alternating relatively warm and cold daily air temperatures caused these lenses to collapse on each other, occupying space in backwaters with tilted and fractured pieces of ice. This phenomenon of ice lensing did not occur in Reach 1 because relatively warm water temperatures and the absence of extremely cold air temperatures precluded diel formation of ice lenses. Ice lensing was also not observed in Reach 3 because of the lack of flow fluctuation and the more consistent water temperatures. Backwaters in Reach 3 often had multiple ice layers (not ice lenses) created by periodic ice jams temporarily raiging river stage. Ice development on backwaters in Reach 3 was greater than in the two upstream reaches because of a lack of daily flow fluctuation and more constant cold water temperatures. 17