Via Chris Brooks, an interesting discussion of legislation in Arizona that appears aimed at making it harder to leave water in rivers for its own sake:

The motivation for preventing the growth of instream flow rights appears to stem from the fact that they have become, in practice, more powerful than they appear on paper. Contrary to the deference that these junior rights must theoretically pay to senior rights is the “no-harm” rule for transferring surface water rights. This rule requires the applicant to consider the potential impacts of a proposed transfer on both junior and senior rights alike. Therefore, new instream flow rights establish a standing in the watershed that can be used to oppose the severance and transfer of existing surface water rights — even if those rights are the most senior in the system. In other words, the proliferation of instream flow rights threatens the ability of existing surface water right holders to manage their rights and could potentially effectively “lock” existing rights to their current place and purpose of use indefinitely.