GEF

Unit 2  |  Water Science and the Water Cycle 61 resources. Other dead zones can be found offshore in countries around the world. Using a watershed framework, we can begin to reduce these dead zones by minimizing fertilizer use and preventing agricultural and urban runoff within watersheds. 2.6  Unit Review ■■ Water has unique chemical properties that make it essen- tial to life on Earth. ■■ Available fresh water is extremely limited and is distributed very unevenly on Earth. The water cycle is the movement of water through earth systems. ■■ Aquatic ecosystems, including wetlands, lakes, and rivers, are vital to human survival and are under threat. ■■ In many developed countries, point source water pollution is less severe than it once was, but nonpoint source pollu- tion remains a major problem. Water pollution of all kinds is still a serious problem in developing countries. ■■ A watershed framework can help us connect to our water resources and the people that share them.