forest to allow for farming in the new settlements, with mixed results. The displaced people later complained that the government had not met its promises in the amount of land allocated. The government denied making such promises, and stated that the people had not owned the flooded land since time immemorial and therefore were not entitled to compensation, although land had been provided. Environmental issues The reservoir waters have been changing from oligotrophic to eutrophic due to increased release of nutrients from submerged organic matter, combined with thermal stratification, making them less hospitable to many fish species. Land clearance around the reservoirs has caused increasing silting, and human activities have caused pollution from sewage, trash, fertilizers and pesticides. The dams have also affected populations of some species of fish and crustaceans in the tributary rivers by disrupting their migration patterns. References Dams in Mexico Buildings and structures in Oaxaca Dams completed in 1989 Papaloapan River