Between 1972 and 1987, Canada and the United States established a complex regime for the protection of the Great Lakes, the largest body of fresh water on the planet. The Great Lakes Water Quality Agreement is an executive agreement that acknowledges that the two countries depend on each other for the well being of the Great Lakes. The agreement has evolved in three phases, each with its own character. The first phase was from 1972 to the renegotiation of a new agreement in 1978. The second phase, from 1978 to the addition of a new protocol in 1987, was dominated by confirmation of the complexity and seriousness of toxic contamination of the ecosystem, and by growing public concern about how this problem could be managed. The third phase, from 1987 to the present, brought major changes in relationships with the International Joint Commissions and in the operations of the agreement's institutions that are still evolving.