Bayou Lafourche is the only fresh water source for the population (150,000) of several Parishes in South Louisiana. It is presently under stress due to increased navigation, flooding, and industrial use. The Bayou was modeled both hydrologically and from a water quality viewpoint. Tides and winds proved to be the most influential factors in the movement of the stream, and these factors, coupled with the complexity of the Canal-Bayou-estuary network, generated a unique modeling effort. Baseline biological indices were established for the Bayou. An attempt to correlate all measured parameters including chemical, biological and hydrological, was made. Water needs through 1980 were predicted.