How the 2007 Interim Guidelines and Drought Contingency Plans Cut Colorado River Deliveries

The rules that automatically reduce water allocations when Lake Mead and Powell drop below critical levels.

By Garret Merkley · Explainer · Aug 17, 2026

Branched from Colorado River Water Distribution: Which States Get How Much and Why

Quick take

The 2007 Interim Guidelines set up automatic cuts tied to Lake Mead elevation, reducing water to Arizona, Nevada, and California when supplies fall short.
Drought Contingency Plans (2019) added a new mechanism: states voluntarily cut water to avoid deeper mandatory reductions and preserve lake levels.
These rules transformed the Colorado River from a fixed-allocation system into one that shrinks deliveries based on actual water availability.

The 2007 Interim Guidelines are a set of operational rules that automatically reduce Colorado River water deliveries to the Lower Basin states (Arizona, Nevada, and California) when Lake Mead falls below certain elevation thresholds. Rather than waiting for a crisis, these guidelines create a tiered system of cuts that kick in at predetermined water levels, turning the Colorado River from a system of fixed promises into one that contracts when the supply shrinks. The 2019 Drought Contingency Plans then added a voluntary layer on top: states agree to cut more water than the guidelines require in exchange for keeping the lake from dropping even further.

How the 2007 Interim Guidelines Work

The 2007 Interim Guidelines use Lake Mead elevation as the trigger. When the lake sits above 1,075 feet, there are no cuts—states receive their full allocations. But as the lake drops, cuts begin. At 1,075 feet, Nevada loses 25,000 acre-feet per year. At 1,050 feet, both Nevada and Arizona face cuts: Nevada loses an additional 25,000 acre-feet, and Arizona loses 320,000 acre-feet. At 1,025 feet, Arizona loses another 130,000 acre-feet. California, historically the senior priority holder, faced no mandatory cuts under the 2007 guidelines alone—a key point of contention.

The system is purely mechanical. It does not require negotiation or political agreement each time the lake drops. Once the elevation falls below a threshold, the cut applies automatically. This predictability was meant to give states time to plan and adjust, rather than facing surprise reductions. However, the guidelines also included a 'shortage sharing' provision: if Lake Powell (the upper basin reservoir) also drops too low, the upper basin states face cuts that can cascade downstream, further reducing lower basin supplies.

The 2019 Drought Contingency Plans: Voluntary Cuts to Avoid Worse Ones

By 2019, it was clear that the 2007 guidelines alone would not prevent Lake Mead from falling to catastrophic levels. The Drought Contingency Plans, signed by Arizona, Nevada, and California (and supported by the federal government), created a new deal: states voluntarily cut water beyond what the 2007 guidelines require, in exchange for federal funding and a commitment to keep the lake from dropping below 1,020 feet. Arizona, which faced the largest mandatory cuts, agreed to cut 192,000 acre-feet per year voluntarily. Nevada and California also made voluntary contributions. In return, if the lake stays above 1,020 feet, the states avoid triggering even deeper cuts that would have been necessary under the 2007 rules alone.

The DCP is essentially a bargain: cut now, voluntarily, to prevent a worse squeeze later. It also included provisions for the upper basin (Colorado, Utah, Wyoming, New Mexico) to make their own contingency cuts if Lake Powell drops too low, ensuring the system does not collapse at either end. These plans were meant to run through 2026, at which point they would need to be renegotiated—a deadline that has already become contentious as the drought persists.

Why This Matters and When It Applies

For over a century, the Colorado River Compact of 1922 promised the Lower Basin states a combined 7.5 million acre-feet per year. That promise was based on a wet period; the river's actual average flow is closer to 12.5 million acre-feet per year, and in drought years it can be much less. The 2007 Interim Guidelines and 2019 DCPs are the first mechanisms that actually reduce deliveries when reality falls short of the promise. Without them, the system would have faced a choice: let the lakes drain completely, or impose cuts with no legal framework. Instead, cuts happen automatically and predictably.

These rules apply whenever Lake Mead is below 1,075 feet—a condition that has been nearly constant since 2000. They affect millions of people in Arizona, Nevada, and California who depend on Colorado River water for drinking water, irrigation, and hydropower. Agriculture in Arizona and the Imperial Valley in California, along with Las Vegas's water supply, all feel these cuts directly. The rules also affect the upper basin states indirectly, because cuts to the lower basin can trigger cuts upstream.

Key Elevations and Cut Thresholds

Above 1,075 feet: No mandatory cuts (full allocations)
1,050–1,075 feet: Nevada loses 25,000 acre-feet/year; Arizona loses 320,000 acre-feet/year
1,025–1,050 feet: Arizona loses an additional 130,000 acre-feet/year
Below 1,025 feet: Additional cuts possible; Lake Mead has not been this low in recorded history
Drought Contingency Plans add voluntary cuts above and beyond these thresholds to keep the lake above 1,020 feet

Why does California not face cuts under the 2007 guidelines?

California holds the most senior water rights on the Colorado River, dating to the 1922 Compact. Under the law, junior rights holders (Arizona and Nevada) must cut first. The 2019 Drought Contingency Plans did get California to make voluntary cuts, but it is not legally obligated to do so under the 2007 rules alone. This has been a major source of friction among the states.

What happens if Lake Powell (the upper basin reservoir) also drops too low?

The 2007 Interim Guidelines include a 'shortage sharing' provision. If Lake Powell falls below 8,500 feet elevation, the upper basin states must cut releases to the lower basin, which means less water flows downstream to Arizona, Nevada, and California. The 2019 DCPs extended this logic: upper basin states agreed to make voluntary cuts if Powell drops below certain levels, to avoid triggering even deeper mandatory cuts.

Are these cuts permanent, or do they end when the drought ends?

The 2007 Interim Guidelines are permanent operational rules; they apply whenever Lake Mead is below 1,075 feet, regardless of cause. The 2019 Drought Contingency Plans, however, were designed to run through 2026. After that date, the states and federal government must negotiate new arrangements. Given the persistence of the drought, that renegotiation is already underway and highly contentious.

How much water is actually being cut because of these rules?

As of 2023, Arizona has been under the largest cuts, losing over 500,000 acre-feet per year (roughly 20% of its allocation). Nevada has lost roughly 25% of its allocation. California, under the voluntary DCP, has committed to cuts but has not faced the same percentage reductions. The exact total depends on Lake Mead elevation, which fluctuates seasonally and year to year.

What happens if Lake Mead keeps dropping and reaches dead pool?

Dead pool is when Lake Mead drops below 1,050 feet, the elevation at which water can no longer flow downstream through the dam. At that point, the system collapses—no water can be delivered to Arizona, Nevada, or California, and hydropower generation stops. The 2007 guidelines and 2019 DCPs are designed to prevent this, but if the drought persists and voluntary cuts are not deep enough, it remains a possibility.

Sources

U.S. Bureau of Reclamation, 'Colorado River Interim Guidelines for Lower Basin Shortages and Coordinated Operations for Lakes Mead and Powell,' 2007.
U.S. Bureau of Reclamation, 'Drought Contingency Plans for the Colorado River Basin,' 2019.
Arizona Department of Water Resources, Colorado River water allocation and shortage data, 2023.