The line above the line

The one idea

A compact is a contract between states, ratified by their legislatures and by Congress. It says how an interstate stream is divided. It does not care about anyone's priority date, because it is not part of the priority system — it sits above it. When Colorado owes water at a state line, the State Engineer has to find that water inside Colorado and stop people from taking it.

Which means a perfectly valid, perfectly senior, perfectly in-priority right can still be curtailed — not because someone older called the river, but because the state has a delivery to make.

Nine of them

Colorado is the most upstream state in the West: four major river systems begin here and leave for somewhere else. That geography is why Colorado has more of these agreements than almost anyone, and why nearly every basin in the state has one sitting over it.

Each one, the streams it governs, and live flow at the gages on them →

Why the gages are in other states

If you look at Colorado water data long enough you will find gages in Nebraska, Kansas, New Mexico, Utah and Wyoming sitting in Colorado's own records. That is not an error. A delivery obligation has to be measured, and the place to measure what left Colorado is at or below the state line. So Colorado keeps watching the river after it stops being Colorado's.

This is also why those gages need reading carefully. A declining trend at a gage in New Mexico is a fact about the Rio Grande in New Mexico. It is not a fact about Colorado's hydrology, and it should never be counted as one — which is exactly the mistake this site made, and fixed, when it first put every gage on one map.

What compliance actually costs

Compacts are not abstractions that live in a filing cabinet. They reach down and change what happens at individual headgates and wells:

• On the Republican, meeting the compact meant retiring irrigation wells and building a pipeline to deliver water to the state line.
• On the Arkansas, decades of Supreme Court litigation with Kansas turned on whether Colorado's well pumping was depleting stateline flow — and reshaped how the state administers wells.
• On the Rio Grande, the annual delivery obligation rises and falls with the year's supply, so what the valley may use is re-set every year.
• On the Colorado River, the 1922 division of a river that turned out to carry less water than its authors assumed is the reason "curtailment" is discussed as a live possibility for the whole Western Slope.

In each case, water users well inside Colorado — holding good decrees, in priority under state law — had what they could take changed by an agreement signed before most of them were born.

Three things that are not compacts

These get lumped together and they work differently:

• A Supreme Court equitable apportionment is a judgment imposed on states that could not agree — Colorado has two, on the North Platte and the Laramie.
• A treaty binds the United States, not Colorado directly, though the water still has to come from somewhere. Two of them cover deliveries to Mexico.
• A transbasin diversion is engineering, not law. It moves water across a divide; it does not change anyone's share. That has its own lesson.

What this does not let you conclude

This lesson explains how compacts work; it does not tell you the terms of any of them. Delivery schedules, index gages, credits and debits, and whether Colorado is in compliance today are all matters for DWR and the compact commissions, and nothing on this site computes them. The assignment of a gage to a compact on our compacts page is ours, made by basin, and has not yet been checked by anyone who administers these agreements. Advisory reading aid on public data — never an administrative or legal conclusion, and never a substitute for DWR administration or an engineer’s analysis. Our methodology has not yet had outside expert review: how this is built.