Water withdrawals and climate change are having significant impacts on riparian food webs, according to a study published Oct. 14, 2010, in Science Express (and expected to be published in Science in November 2010).
One of the more prominent impacts is a major shift in top fish predators, with the effects depending on whether the waterway has been subject to short-term drought, long-term drought, or sudden deluges of water. In the situations where the top predators are reduced or eliminated, there can be noticeable short-term effects on people, through the reduced availability of fish caught for food or sport (such as bass, trout, salmon, pike, and shrimp), and long-term changes in riparian ecology — including shorter food chains — that affect both people and the rest of the environment, sometimes in unpredictable ways.
- "The Role of Discharge Variation in Scaling of Drainage Area and Food Chain Length in Rivers,"  Lead author, John Sabo,  Arizona State University, cell 480-734-7120; co-author, Ted Kennedy,  USGS, 928-556-7374, cell 928-699-9115. Oct. 15, 2010, press release. 
The study was based on findings in 36 North American waterways, both major and minor, which are specified in a supplement to the study (see Table S1). In general, the water basins included portions of the Great Lakes-St. Lawrence River, the Hudson-Delaware river basins in New York, the MississippiRiver basin, the desert Southwest, PacificCoast waterways, and Alaska and Puerto Rico.
The authors speculate that similar impacts could be occurring in waterways around the world. Many experts have been documenting dramatic changes in water flows as human demand steadily increases and as water supply becomes more erratic and unpredictable, often punctuated by extreme weather events such as drought and floods.