A salinity and velocity section across the interface between the freshwater layer and the salt wedge in in the Mississippi River. Isohalines are spaced 2 units apart, and a change of salinity of 4 is indicated by a colour change. The salinity in the lower layer is still far from oceanic; the Mississippi delta has several mixing regions, and water in the lower layer can be quite brackish.

Note the change in current direction across the interface between the two layers. It indicates clearly that water is drawn into the interface from both layers and removed towards the sea by rising in the interface and moving outwards. (The red dot indicates an observation of zero velocity.)

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