There's an analysis of instream water rights issues in Arizona on the Montgomery & Associates Arizona Water Policy Update website, titled, "Why would anyone want to inhibit the development of instream flow rights in Arizona? The answer is more complex than it may seem.."
Authors Juliet McKenna, Taylor Shipman, and Michele Robertson explains that "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." [Photo credit, AZ DEQ]