The US Supreme Court on Monday held [opinion, PDF] that the US government had the authority to bring an action against New Mexico alleging that they violated the Rio Grande Compact [statute], an agreement between Colorado, Texas and New Mexico to perpetuate the equitable division of water from the Rio Grande River.

The compact, approved by Congress in 1939, requires Colorado to deliver a specified amount of water annually to New Mexico at the state line and directs New Mexico to deliver a specified amount of water to a reservoir 100 miles inside its border. The reservoir was completed in 1916 as part of the federal government’s Rio Grande Project and plays a central role in fulfilling the US’ obligations to supply water under the Distribution of Waters of Rio Grande [text, PDF], a 1906 treaty with Mexico, as well as under several agreements with downstream water districts in New Mexico and Texas.

The action, first initiated by Texas, claimed that New Mexico effectively breached its Compact duty to deliver its share of water to the required common pool by allowing downstream New Mexico users to siphon off water below the reservoir in ways the downstream water agreements did not anticipate. The US government then followed by filling parallel allegations to those of Texas.

In response to the complaints, New Mexico filed a motion to dismiss stating that the US government did not have the authority under the Compact to enforce its terms. Adding another layer to the dispute was Colorado, which maintained that the US government should be permitted to pursue claims only to the extent they arose under the original 1906 treaty with Mexico, and not under the subsequent Compact.

Writing for a unanimous court, Justice Neil Gorsuch stated:

[W]e have sometimes permitted the federal government to participate in compact suits to defend “distinctively federal interests” that a normal litigant might not be permitted to pursue in traditional litigation… Viewed from some sufficiently abstract level of generality, almost any compact between the States will touch on some concern of the national government-foreign affairs, interstate commerce, taxing and spending. No doubt that is the very reason why the Constitution requires congressional ratification of state compacts…. [W]e are persuaded these factors favor allowing the United States to pursue the Compact claims it has pleaded in this original action.

Both claims for the US government and Texas have been remanded to the lower courts for further proceedings.