The objective of the research is to develop estuarine system management models based upon discrete-time stochastic optimal control. An analytical feedback control law is given. The control law enables the decision-makers to determine the optimal upstream reservoir releases during a month after the salinity and nutrients levels in the estuary are observed at the beginning of the month. Two types of estuarine systems are considered. One is a lumped-parameter system. Another is a distributed-parameter system described by a two-dimensional hydrodynamic and salinity transport finite difference numerical model (HYD-SAL). The proposed estuarine system management models are applied to the Lavaca-Tres-Palacios Estuary in Texas.