Technical Abstract: In the process of storing, diverting, transporting, irrigating, consuming, and draining water, the natural hydrology of a watershed is changed significantly. These changes impact the natural environment. River flows are altered and reduced and sometimes depleted; groundwater levels may be lowered by pumping or raised by over irrigation; wetlands may be created or dried up. Drainage waters from agricultural lands are usually of poorer quality than the applied water and may carry both agricultural chemicals and naturally occurring substances into groundwater, rivers, and lakes. Nitrogen and pesticides leach to groundwater, and sediments, phosphorus, and agricultural chemicals can move with surface runoff to rivers and lakes. Erosion and salinization may damage agricultural lands. Although many of the environmental impacts of irrigation are negative, irrigation plays a critical role in providing food and fiber for our growing population. Most of the world's fruits and vegetables are grown with irrigation. Providing the same food without irrigation would likely have even greater environmental impacts.