Explanations for the emergence of the Aztec state need to consider changes in the climate and the potential effects resulting from these changes on the productivity of the lake network in the Valley of Mexico. Change in the human ecosystem is a complex process of interactions between multiple cultural variables and the environment. In this study, I examine the nature of three primary resources, fish, salt, and waterfowl, available for Early Aztec–period exploitation within the valley lake system. The intensification of lacustrine resource exploitation appears to be correlated with changing climatic conditions that occurred about a.d. 1150. Although the focus of this study is be on the cause-and-effect relationship between culture and environment, it is acknowledged that the environment is just one factor that must be considered to fully understand initial Aztec development.