This study evaluates the physicochemical degradation of Lake Patzcuaro (Mexico), driven by agro-industrial expansion—with 4,806 hectares of new avocado monocultures—and by untreated urban wastewater discharges. Based on multiparametric primary field data collected between 2019 and 2026, including radial sampling around Tecuenita Island, critical anomalies were identified, such as temperatures reaching 31°C, extreme alkalinity with pH levels of 12, and severe hypoxia with dissolved oxygen below 1 mg/L. The comparative historical analysis shows that water quality parameters far exceed current national standards, with electrical conductivity above 1,000 µS/cm, turbidity of 225.6 NTU, and an organic load of 16.3 mg/L BOD₅. The loss of 684 hectares of biofiltration wetlands in the basin correlates directly with the lake’s advanced hypereutrophic state, characterized by high concentrations of fecal coliforms and recurrent algal blooms. The results highlight the urgent need for effective environmental governance and concrete hydrological restoration measures to halt a degradation process that, if allowed to continue, will likely become irreversible.