Article V authorizes interstate negotiation through a convention, but other forms of interstate negotiation occur very frequently. One form is represented by the long-lived Uniform Law Commission, a standing body of state representatives that drafts and prepares standard statutes for state legislative consideration and adoption. (The best known of these statutes is the Uniform Commercial Code, but there are many others.)
In 1922, the seven Colorado River states and the federal government met in convention (called a “commission”) to negotiate the Colorado River Compact, and over the course of several years (1946-49) the five Upper Colorado River states and the federal government met in recurring convention to work out a compact among themselves.
However, those agreements only began to solve water allocation and control issues. More recent Colorado River agreement have been negotiated in other ways.
In 2004, at the prodding of the U.S. Secretary of the Interior, the signatories to the 1922 compact began a series of negotiations that did not, however, occur in a convention framework. Discussions occurred in personal meetings, facilitated by email and, probably, by telephone calls. The federal government did not participate directly in these discussions, as it did in the 1922 and 1946-49 negotiations.
On the other hand, there were important non-state participants: water districts and authorities that were, for the most part, the real parties in interest. Finally, an agreement among the states was signed in April, 2007. The agreement (called “Colorado River Interim Guidelines”) was “affirmed” by the states in December, 2007, and substantially adopted through a formal Record of Decision by the Secretary of the Interior.
We are grateful to Tom McCann, Deputy General Manager of the Central Arizona Project, for this information. A newspaper article reporting on the agreement is located here. Mr. McCann also tells us that this negotiation “process is typical of how agreements are developed within the Colorado River basin” and that the “2007 Basin States’ Agreement is but one of many agreements that collectively make up the Law of the River.”