Fresh water discharge into Todos os Santos Bay is assessed on the basis of measured and estimated river discharge data. The average mean fresh water discharge amounts to 111.1 m3s-1, and might be added to another 28.2 m3s-1 that falls directly on the bay area as rainfall. The mean river discharge represents only 0.08% of the spring tidal prism, calculated by the means of a through analysis of the depth area distribution.