Lake Patzcuaro is a tropical, high-altitude, freshwater lake (130 km2surface area) located on the Mexican plateau. The lake originated from tecto-volcanic processes associated with the Mexican Neovolcanic Axis. Maximum depth (12 m) occurs in the northern part of the lake, whereas shallow areas are developing in the south. Its indigenous fish fauna and the presence of P'urhépecha Indian settlements around its shoreline identify Lake Patzcuaro as a unique natural resource having ecological, historical, and cultural value. The lake is endorheic and the annual water balance is controlled by differences among rainfall, seepage, watershed runoff, and evaporation. A mass-balance model indicates that hydrologic inputs from the watershed are being reduced as a result of watershed deterioration. High turbidities result from volcanic silt, raw sewage, and increasing erosion loads to the lake. Lake Patzcuaro is light-limited due to scattering and attenuation from suspended inorganic materials. The lake has high concentrations magnesium, sodium, carbonates, total phosphorus, chlorophylla, and suspended solids. Lake Patzcuaro is mostly eutrophic with some less productive areas. Proposed lake management strategies focus on the watershed and include: erosion control and reforestation, basin-wide sewer systems and wastewater treatment, and preservation of the indigenous fishery.