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<br />I .... <br />J <br /> <br />chora of statutes portends a serious federaLis~ conflict on tile Colorad0 <br /> <br />- <br /> <br />River. The basic quality problem on the river is salinity--increased concen- <br /> <br />tration of dissolved solids.65 The problem has many natural causes but is <br /> <br />exacerbated by human activity. Already highly saline water is made worse by <br /> <br />the evaporation of water stored and slowed by dams, causing exposure of larger <br /> <br />surfaces for longer times, and by addition of agricultural return flows that <br /> <br />become increasingly concentrated as waters are reused and ,as they leach salts <br /> <br />J <br /> <br />from cultivated fields. <br /> <br />The federal government has dealt with water quality problems selectively. <br /> <br />- <br /> <br />The federal role in controlling water pollution is greatest under the Clean <br /> <br />- <br /> <br />66 <br />Water Act. The Act requires the government to set effluent standards re- <br /> <br />stricting the amounts of various pollutants that can be discharged from "poiot <br /> <br />sources" such as pipes and ditches. Irrigation return flows contain agricul- <br /> <br />tural chemicals (as well as dissolved solids) that can cause serious pollution <br /> <br />b7 <br />problems, but for political reasons, Congress has chosen not to regulate <br /> <br />agricultural return flows, removing them from the definition of "point <br />.. d 68 I' b <br />sources un er the Clean Water Act. t ~s possi le) though not likely, that <br /> <br />.... <br /> <br />Congress will close this, the largest gap in the coverage of the Act. Doing <br /> <br />so could have dramatic effects on irrigation practices. Return flows either <br /> <br />would have to be treated or irrigators would be limited in the amount of land <br /> <br />that could be irrigated. <br /> <br />The Clean Water Act also includes a provision for federal exercise of <br /> <br />1 h 11 1. - 69 <br />authority to contro t e overa water qua lty ot streams. The job belongs <br /> <br />in the first instance to the states, but if they do not take sufficient action <br /> <br />70 <br />declined to do so on the Colorado. <br /> <br />to preserve water quality, the United States may intercedeQ ah-h<>tl&l) it has <br />'" <br /> <br />Diversion of too much water from the <br /> <br />stream comhined with evaporation and transpiration can increase the concen- <br /> <br />- 20 - <br />