Ice collapse in slough below Willow Island A section of ice in this slough that dropped due to a decrease in water level since initial ice formation in the fall. As the water level under the ice decreases through the winter, the ice is left with nothing holding it up from below. Process Observed: Ice CollapseWater Level Drop Date Process Observed: Friday, March 30, 2007 Galleries: Slough below Willow Island Gallery