The dynamics of a large tropical lake, Lake Maracaibo, Venezuela, are described using field data and the 3D Estuary and Lake Computer Model (ELCOM). ADCP data from November 1998 and CTD data spanning September 1998 to April 1999 are presented. Seawater enters Lake Maracaibo via an augmented natural connection to the Gulf of Venezuela, which allows an influx of seawater and results in almost perenial salt stratification within the lake. Spatially varying wind forcing is found to be necessary to simulate an observed basin-scale cyclonic gyre. The gyre maintains a doming of isopycnals through a geostrophic balance that lifts high-salinity bottom water closer to the surface where it is entrained into the surface mixing layer and subsequently advected by wind-induced circulations. Horizontal excursions of saline bottom water result in considerable variability of salinity stratification at any given location in the lake. September to December (wet season) was characterized by relatively high river inflow and weak winds, resulting in weak forcing of lake circulation and weak basin-wide vertical salt flux. January to April (dry season) was characterized by relatively weak river inflow and strong winds, resulting in strong forcing of lake circulation and enhanced, basin-wide vertical salt flux. The dry season of 1999 was relatively wet (compared with other dry seasons, but still drier than the previous wet season) and there was no indication of a saline underflow occurring from Maracaibo Strait into Lake Maracaibo. The combination of strong wind forcing, low river inflow (compared with the wet season), and little or no saline intrusion during the dry season of 1999 resulted in almost complete flushing of saline bottom water.