An estuarine turbidity maximum, or ETM, is the zone of highest turbidity resulting from turbulent resuspension of sediment and flocculation of particulate matter in an estuary. The turbulence is driven by tidal forces, waves, and density-drive currents that push a salt wedge upstream and beneath outflowing freshwater discharge. An estuarine turbidity maximum, or ETM, is the zone of highest turbidity resulting from turbulent resuspension of sediment and flocculation of particulate matter in an estuary. The turbulence is driven by tidal forces, waves, and density-drive currents that push a salt wedge upstream and beneath outflowing freshwater discharge.