The mixed Lagrangian and Eulerian approach is proposed to study the thermal and hydraulic performance of cooling ponds that are used mainly to dissipate the waste heat from power plants into the atmosphere. The hydraulic behavior of the cooling pond is analyzed by the Eulerian method, and the Lagrangian approach is used to study the thermal distribution, ‘Isotime’ lines are obtained by numerically solving the governing hydrodynamic equations. The Lagrangian temperature is obtained by solving the energy equation either numerically with the fourth‐order Runge‐Kutta method or analytically with the linearization of the net heat flux at the water surface. The Lagrangian temperature is then converted to the Eulerian temperature through the isotime lines. This model is applied to predict flow patterns, isothermal lines, and discharge temperature for a cooling pond in the southwestern United States.