River basin development generally calls to mind the Tennessee Valley, the Missouri Valley, the Colorado Valley-large areas, covering several states or parts of states. Attention focuses on the basin and on the role that rivers, once thought of as barriers, have come to play as nationally or regionally unifying forces. The over-all problems seem, at first blush, primarily to be federal ones that transcend purely state or local interest. But the fact is that rivers form and cross the boundaries of several states, and these states, thus, have exerted and will continue to exert a great influence an their development. Moreover, no matter how unified a basin plan may appear to be as a whole, it is composed of many separate subbasins and projects which may be totally contained within a single state and which must be internally coordinated as well as externally related to the major basin plan. River basin development, accordingly, is seen to be not an exclusively federal function consisting entirely of the large works constructed by the federal government on the major rivers. The states, their lesser governmental units, and private agencies, too, play an important role. Thus, some states even engage in the actual construction of projects, through such agencies as the Montana Water Conservation Board1 and the state-created authorities that have developed the Texas coastal rivers.2 Irrigation, conservancy, public-power, flood-control, and drainage districts also construct works that individually and in the aggregate make significant contributions to full river basin development.3 And much activity is directed by private interests, ranging from the large coordinated projects of the major power companies, cooperative water companies, and major industrial users to the individual efforts of a single farmer who controls the water on his fields. For the most part, these public and private agencies operate under state law, and these institutional laws, consequently, have an important effect upon river basin development. But the state laws that have even greater influence are those dealing with the private water rights of individuals. Some features of river basin development may, of course, depend wholly upon