Combining two models, researchers studied the hydrology of Mar Menor coastal lagoon. They used the SWAT model to simulate streamflow and the QWET model to estimate the water balance. The models performed well, showing good agreement with observed data. The study found that the lagoon receives more water from the Mediterranean Sea in summer, while in some winter months, it flows back to the sea. The average rainfall over the lagoon is 301 mm per year, with evaporation at 1325 mm per year. Surface runoff and groundwater discharge contribute to the lagoon's water balance, with extreme storm events causing variations in runoff. This approach helps understand the lagoon's hydrology and can aid in developing strategies to prevent eutrophication.