Hydrologic changes of freshwater inflow into estuaries include those factors that affect the quantity and quality of the inflows. The quantity of freshwater inflows reaching an estuary varies depending on the timing, frequency, duration, and extent of the inflows. The qualities of freshwater inflows vary depending on the inputs into the flows upstream and affect the dynamics of estuaries. Quantity and quality of freshwater inflows can be monitored and related to the resulting changes in salinity levels of the estuary.