Frazil ice from upstream can also be deposited under an existing ice cover along the river throughout the winter. Due to the relatively low river bed slope and low turbulence at the delta portion of the river, a juxtaposed ice cover begins at the Slave River Delta and then extends upstream to Fort Smith (Figure 1). Water pockets and air bubbles are also formed, particularly at the upstream portion of the Delta along the stretch between Big Eddy and the Nagle Channel.