Radon 222 concentrations in waters of the Hudson River estuary show little consistent vertical, axial, or seasonal variation. The median of 106 summer measurements is 1.43¿0.25 dpm/1, and the median of 17 winter measurements is 1.30¿0.35 dpm/1. A budget is constructed for the water column which balances the rate of radon input against the rate of radon loss for two regions, one of which is broad and shallow and the other narrow and deep. The primary supply of radon for these two regions is from the sediments (75--90%), with minor inputs from radium 226 decay in the water column, stream runoff, and tidal pumping of groundwater. Loss of radon occurs by evasion to the atmosphere and decay in the water column in roughly equal amounts. The activity of mobile radon in sediments (per wet sediment volume) is 0.33¿0.10 dpm/cm3 in the broad, shallow area of the estuary and 0.42¿0.11 dpm/cm3 in the narrow, deep reach immediately upstream. When these value are used, the flux supplied by molecular diffusion is approximately 40% of the total input. Constant physical stirring of the upper few centimeters of sediments by bottom currents over large areas and stochastic reworking to somewhat greater depth in localized sediment deposits appear to be primarily responsible for augmenting the flux from sediments provided by molecular diffusion.