In parts of the United States far from sea-coasts or large natural lakes, reservoirs built for water supply and other purposes have become the focus of enormously popular forms of recreation that would otherwise be impossible in those regions--sailing and motorboating and water-skiing and the sort of fishing possible only on big water, and such things. Properly designed and located, they can be beautiful bodies of water, as the vacation homes that grow up around many of them testify. Strong objections to them also frequently are voiced. They are one of the most massive manifestations of man's technological ability to adapt natural processes to his use, and they sometimes have profound effects on fish and wildlife and the whole ecology of a stream system region, to the dismay of many conservationists. Often too they flood out large areas of riverbottom farmland and other private property, arousing the ire of some rural folk and small townsmen who feel that their interests have been sacrificed to the water or flood-protection demands of downstream city dwellers. Opponents of major dams sometimes assert that many of them have been built not to meet real hydrological needs but to foster economic development which may or may not materialize and may or may not be worth the loss of natural or scenic or agricultural resources disrupted by the reservoirs. Other thinkers, not necessarily against reservoirs in general, express a doubt that the potential effects of specific structures are always thought out sufficiently beforehand. Among these are the authors of a recent publication of the National Academy of Sciences--National Research Council, _Alternatives in Water Management_: "_We create great reservoirs that stop the migration of fish and then provide costly fishways, hatcheries, and other devices to maintain the fishery, and with no certainty of success. We impound water without knowing the effects of that impoundment on its quality. We build an irrigation project and then find salinity increasing dangerously in the river downstream. We eliminate high-flood peaks by reservoir storage, but downstream from some reservoirs we see unpredicted erosion, sedimentation, bank-cutting, and other effects, even unto, as in California, the loss of beaches along the seacoast, starved of their supply of sand._"