Hydrologic balance of Lake Chapala (Mexico)

Lake Chapala, whose primary tributary is the Rio Lerma, is the largest fres hwater lake in Mexico and for the past 95 years has maintained an average s torage capacity close to 6,700 Mm(3). Starting in the early 1970s, the Lerm a-Chapala basin rapidly industrialized. In response to these upstream anthr opogenic activities, the fisheries, aesthetics, and water quality of Lake C hapala have decreased as a consequence of the increasing chemical and biolo gic pollutants mainly from the Rio Lerma. Additionally the growth of Guadal ajara has resulted in increasing potable water demands on the lake to satis fy a population currently greater than 4.5 million. During the 1980s, the o utflow and water losses from the lake substantially exceeded the inflow and other water contributions. In this paper, the recent behavior of the hydro logic and bathymetric parameters of Lake Chapala are summarized and some im portant physical stresses on the system are identified. The focus of this w ork is the 1934-1989 period, and it is shown that starting around 1980 some of the main contributors to the lake water balance were severely perturbed and the lake reached its second lowest recorded level. The disturbances of the system are so severe that the entire regional ecosystem could be irrev ersibly affected in the near future.