| Summary: | Under ice river plume data were collected in the spring of 1988 and 1990 at the mouth of the Great Whale River, Hudson Bay, Canada. Tidal analysis of tide gauge data and predicted tides shows a phase advance and amplitude decrease of the tide under continuous landfast sea ice. Current meter and echosounder measurements, as well as temperature-salinity profiles were taken within the first 2 km off-shore of the river mouth to provide a detailed picture of the nearshore plume conditions. Stable, subcritical flow conditions were observed for most of the sampling period, with the buoyant freshwater plume maintaining a depth of about 4 m almost continuously. During spring low tide (the lowest low tide), the cross-sectional area through which the river discharge must flow decreases substantially, resulting in supercritical (Froude number $>$1) conditions over some periods and the formation of an internal hydraulic jump.
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