The Patos Lagoon is located in the southernmost part of Brazil, between 30°–32° S and 50°–52° W, being connected to the South Atlantic Ocean via a narrow channel that is less than 1 km wide. The lagoon drains a hydrographic basin of approximately 200,000 km², and its principal rivers contribute with an annual mean discharge of about 2000 m³ s⁻¹. In this work, the dynamics of the Patos lagoon coastal plume was studied considering theoretical situations that determine the relative importance of Earth rotation, river discharge, tides, and winds. To carry out this analysis, the finite element model TELEMAC2D was used for the experiments. The results show that Earth rotation is very important in generating asymmetry in the plume flow. Tides are important for the mixing processes, causing an increase of the plume area and a decrease of the plume penetration offshore. In addition, results also showed that northeast winds displace the coastal plume southward, which is likely to be related to the formation of mud banks south of the Patos Lagoon mouth. During southwest wind events, the mixing zone moves landward, being observed inside the access channel, while part of the coastal plume remains in the coastal zone and is directed northward as a coastal current.