As they relate to water resources, different types of compacts and interstate agreements are intended to equitably divide and apportion waters within and between states in order to settle existing or future controversy concerning the utilization of those waters. Colorado has numerous intrastate agreements among its stakeholders, and in terms of its interstate waters, nine interstate compacts, two Supreme Court equitable apportionment decrees, two memoranda of understandings/agreements and two international treaties govern how much water the state is entitled to use and consume (Colorado Division of Water Resources [DWR], 2006; Colorado Water Conservation Board [CWCB], n.d.; State of Colorado, 2015; Colorado Foundation for Water Education [WEco], 2015). Although these different compacts and agreements determine the amount of surface water allocated between and within each state, due to the connected, inter-dependent nature of surface and groundwater, they also impact how much groundwater can be pumped by each state.

The following sections outline a few of Colorado’s intrastate compacts, its nine interstate compacts, two Supreme Court equitable apportionment decrees, two memoranda of understandings/agreements and two international treaties.

Intrastate agreements are between parties to allocate water within the state among stakeholders. Intrastate agreements help Colorado stakeholders align key parties’ interests and understanding so that the state has a united voice when dealing with interstate and federal negotiations and litigation about water exiting the state. These agreements benefit the individual stakeholders, but also equip the state to effectively protect state interests in interstate matters (State of Colorado, 2015).

The following are a few examples of intrastate agreements within Colorado, including a list of the state’s 44 major diversions. For more detailed information on these agreements, see Chapter 8 (“Interbasin Projects and Agreements”) of the 2015 Colorado Water Plan.

Arkansas River Voluntary Flow Agreement

Established in 1990, the Arkansas River Voluntary Flow Agreement is a voluntary flow management program partnership among Colorado Parks and Wildlife, Southeastern Colorado Water Conservancy District, Pueblo Board of Water Works, Trout Unlimited, the Arkansas River Outfitters Association and the Bureau of Reclamation. The agreement helps meet the environmental and recreational needs of the Upper Arkansas Basin by providing increased recreational flows on the river and beneficial flows for wildlife.

Map of the Arkansas Basin.
Arkansas River Basin. WestWater Research, LLC (2014).

Colorado River Cooperative Agreement

Completed in 2013, the Colorado River Cooperative Agreement is the culmination of years’ worth of negotiation between Denver Water and several western slope entities with the goal of to protect Colorado River watersheds while allowing Denver Water to develop future supplies. More than 40 stakeholders, including water providers, county commissioners, local municipalities, ski resorts and environmental groups, participated in the process alongside the 18 signatories.

Map depicting the Colorado River Cooperative Agreement area.
Colorado River Cooperative Agreement Map. Colorado River District (2011).

Windy Gap Firming Project

The Windy Gap Firming Project is a collaboration among 13 northeastern Colorado providers to improve the reliability of water supplies from the Windy Gap Project. The firming project is building a new reservoir called Chimney Hollow on the eastern slope to provide dedicated storage to supply a reliable 30,000 acre-feet of water each year, supplied via the Colorado-Big Thompson Project. This collaboration between eastern and western slope entities and state agencies will improve the conditions for aquatic life on the Colorado River, as well as help the Windy Gap Firming Project progress toward meeting water supply needs on the eastern slope.

Map of the Windy Gap Firming Project.
Windy Gap Firming Project. Northern Water (2011).

Colorado has 44 major water diversions (Figure 1) that move water from one of the state’s major watersheds to another. Of those 44 diversions, 27 are considered transbasin, whereby the water they transport crosses between two of the state’s four major river basins: the Colorado (Colorado mainstem, Yampa/White, Gunnison and Dolores/San Juan basins), the Platte (North Platte and South Platte/Republican basins), the Arkansas and the Rio Grande. Twenty-five of these 27 diversions cross the Continental Divide (WEco, 2014), and are referred to as transmountain diversions.

CO Transbasin Diversions map

Map of Colorado's transbasin diversions.
From Citizen's Guide to Colorado's Transbasin Diversions by Water Education Colorado (2014).

Colorado Water Diversions

Receiving BasinMap #DiversionMean AF/Yr*First AppropriationSource Stream(s)
South Platte River Basin1Wilson Supply Ditch2,3141896Sand Creek
2Deadman Ditch7271899Deadman Creek
3Bob Creek Ditch911897Bob Creek
4Columbine Ditch1041889Columbine Creek
5Laramie-Poudre Tunnel14,7881902Big Laramie River
6Skyline Ditch4,9991891West Branch Laramie River
7Cameron Pass Ditch1371882Middle Fork Michigan Creek
8Michigan Ditch2,4091902Michigan River
9Grand River Ditch17,4621890North Fork Colorado River
10Adams Tunnel216,5701935North Fork Colorado River
11Moffat Tunnel (includes A.P. Gumlick Tunnel)52,3901921Fraser River tributaries (Cabin, Elk, Hamilton, Hurd, Jim, Meadow,
Ranch, St. Louis & Vasquez Creeks) & Williams Fork River
12Berthoud Pass Ditch6641902Fraser River
13Straight Creek Tunnel3111957Straight Creek
14Vidler Tunnel5181893Peru Creek
15Harold D. Roberts Tunnel58,4261946Blue River
16Boreas Pass Ditch1171937Indiana Creek
17Hoosier Pass Tunnel8,3751930Blue River tributaries (Bemrose, Crystal, Hoosier, Monte Cristo, Silver & Spruce Creeks, & McCullough Gulch)
Arkansas River Basin18Columbine Ditch1,4311930East Fork Eagle River
19Ewing Ditch1,0271880Piney Creek
20Wurtz Ditch2,5081906Eagle River tributaries (Bennett, S. Fork Bennet, Mitchell & S. Fork
Mitchell Creeks)
21Homestake Tunnel25,2861952Homestake Creek & tributaries (Fancy, French, E. Fork Homestake,
Missouri & Sopris Creeks)
22Charles H. Boustead Tunnel52,0131957Fryingpan River & tributaries (Carter, Cunningham, Granite, Ivanhoe,
Lilly Pad, Mormon & Sawyer Creeks, Chapman Gulch, & N. & S.
Fork Fryingpan) & Roaring Fork River tributaries (Hunter, Midway
& No Name Creeks)
23Busk-Ivanhoe Tunnel5,1081952Fryingpan River
24Twin Lakes Tunnel40,0051930Roaring Fork River & tributaries (Grizzly, Lincoln, Lost Man, New York
& Tabor Creeks, & Brooklyn Gulch) & Frying River tributaries
(Ivanhoe & Lyle Creeks)
25Larkspur Ditch1901931Marshall Creek
26Hudson Branch Ditch3521892Medano Creek
27Medano Pass Ditch1,1001892Medano Creek
Rio Grande Basin28Tarbell Ditch4321914Cochetopa Creek
29Tabor Ditch7031910Cebolla Creek
30Weminuche Pass Ditch1,3251934Pine River
31Pine River – Weminuche Pass Ditch4811934Pine River
32Williams Creek – Squaw Pass Ditch2401937Williams Creek
33Don La Font Ditch # 1 & 21911940East Fork Piedra River
34Treasure Pass Ditch2141922West Fork San Juan River
35San Juan – Chama Project92,789n/aRio Blanco
Gunnison River Basin36Red Mountain Ditch981945Mineral Creek
37Carbon Lake Ditch2561954Mineral Creek
38Mineral Point Ditch961956Burrows Creek
39Leon Tunnel1,3731900Middle Fork Leon Creek
Colorado River Basin40Divide Highline Feeder Ditch8821915Clear Fork
41Sarvis Ditch7601911Service Creek
42Stillwater Ditch2,0281903Bear River
43Dome Ditch3001893Dome Creek
44Redlands Power Canal502,4151905Gunnison River
Water Diversions in Colorado. Transbasin diversions moving water between two of the four major river basins are emphasized in boldface type. Mean AF/year figures are based on the period of record available in electronic form for each diversion. Table recreated from "Citizen’s Guide to Colorado’s Transbasin Diversions"
(CFWE, 2014).

Interstate compacts are formal agreements between two or more states agreeing upon water allocation. Such compacts establish the terms for sharing water of an interstate stream and require approval by the states’ legislatures and Congress (DWR, 2006; WEco, 2015). The following outlines Colorado’s nine interstate compacts.

Animas-La Plata Project Compact (1969)

The Animas-La Plata Project Compact is unusual in the sense that it addresses a water project rather than river waters. The compact gives New Mexico equal priority in rights as Colorado to store and divert the project water, providing such uses are within New Mexico’s allocation in the Upper Colorado River Compact. The compact also fulfills settlements to the Ute Mountain Ute Tribe and the Southern Ute Indian Tribe, and provides water to the Navajo Nation.

Map of the Animas-La Plata Project within Colorado & New Mexico.
Animas-La Plata Project. USBR (2007).

Arkansas River Compact (1948)

Instead of imposing fixed-delivery obligations, the Arkansas River Compact protects water uses in existence in 1949, and limits future development in either Colorado or Kansas to the extent that it would cause material depletion of usable state-line flow. The compact also addresses the allocation of benefits from use of storage at John Martin Reservoir, and establishes the Arkansas River Compact Administration to administer provisions of the compact and oversee operations at John Martin Reservoir.

Map of Arkansas River Basin within Colorado & Kansas.
Arkansas River Basin. WEC (2015).

Colorado River Compact (1922)

The Colorado River Compact apportions 7.5 million acre-feet of consumptive use per year to both the Upper and Lower Colorado Basins, but also allows the Lower Basin to increase its consumptive use by 1 million acre-feet per year; therefore, the Lower Basin is apportioned up to 8.5 million acre-feet of consumptive use per year. The Upper states may not cause the flow of the Colorado River at Lee Ferry, Arizona, to be depleted below an aggregate of 75 million acre-feet for any period of 10 consecutive years. The Department of the Interior, Upper Colorado River Commission and governor appointed representatives from each of the Colorado River Basin states monitor and administer the compact. Congress authorized seven states in 1921 to negotiate the compact. Six of them ratified the compact promptly, but Arizona did not join until 1944. An amendment was adopted in 1925 to waive the requirement that all seven states approve. Congress accepted the revision in the 1928 Boulder Canyon Project Act, which however, required California’s approval. California approved the amended compact in 1929.

Map of the Colorado River Basin.
Colorado River Basin. USGS (2016a).

Costilla Creek Compact (1944; revised 1963)

The Costilla Creek Compact establishes uses, allocations and administration of the waters of Costilla Creek in Colorado and New Mexico. The compact gives roughly one third of the water to Colorado and two thirds to New Mexico, with the Costilla Creek Compact Commission administering terms and overseeing compliance. The 1963 amendment reallocated water between two of the ditches on the Costilla Creek system, and also made other minor adjustments to the original compact.

Map of Costilla Creek Compact Boundaries.
Costilla Creek Boundaries. WEC (2015).

La Plata River Compact (1922)

The La Plata River Compact apportions the La Plata River between Colorado and New Mexico allowing each state unrestricted use between December 1 and February 15. Outside of that time period, each state can use the flow of the river at the state line if the flow is in excess of 100 cubic feet per second (cfs). If the flow is less than 100 cfs, Colorado must deliver half of the preceding day’s mean flow at Hesperus, Colorado, but no more than 100 cfs. The state engineers administer the compact.

Map of the La Plata River Basin within Colorado and New Mexico.
La Plata River Basin. WEC (2015).

Republican River Compact (1942)

The Republican River Compact divides the waters of the Republican River Basin among Colorado, Kansas and Nebraska, as well as establishes the Republican River Compact Administration to adminster terms and oversee compliance. Colorado’s consumptive uses are limited to 54,100 acre-feet per year (plus all uses from Frenchman and Red Willow creeks), and allocates 190,300 acre-feet per year to Kansas and 234,500 acre-feet per year to Nebraska; however, if the water supply of any sub-basin varies, the allocations also change.

Map of the Republican River Basin found in Colorado, Nebraska & Kansas.
Republican River Basin. WEC (2015).

Rio Grande Compact (1938)

The Rio Grande Compact allocates beneficial use of water from the Rio Grande River among Colorado, New Mexico and Texas, and provides water to Mexico consistent with the 1906 Treaty. Colorado is obligated to annually deliver a certain amount of water at the New Mexico/Colorado state line based on an index schedule, and New Mexico is obligated to deliver certain amounts to Elephant Butte Reservoir based on a similar, yet separate, index schedule. The compact creates a system of water credits and debits, storage, spills and releases from the Rio Grande Project at Elephant Butte, and places further restrictions on storage within Colorado and New Mexico. The compact also establishes the Rio Grande Compact Commission to administer terms and oversee compliance.

Map of the Rio Grande River Basin highlighting major structures & features found within.
Rio Grande River Basin. WEC (2015).

South Platte River Compact (1923)

The South Platte River Compact establishes Colorado and Nebraska’s rights to use South Platte River water, giving Colorado the right to fully use the water in the lower section between October 15 and April 1. When the flow is less than 120 cfs during the irrigation season, Colorado must curtail diversions in the lower section to any decrees junior to June 14, 1897, from the Washington County line to the state line. The state engineers administer the compact.

Map of the South Platte River Basin.
South Platte River Basin. USGS (2016b).

Upper Colorado River Compact (1948)

The Upper Colorado River Basin Compact apportions a percentage of available river water allocated by the terms of the Colorado River Compact to each Upper Basin states: Arizona – 50,000 acre-feet/year; Colorado – 51.75%, Utah – 23%, Wyoming – 14%, New Mexico – 11.25%. The compact establishes obligations of each Upper Basin state with respect to required deliveries at Lee Ferry, Arizona, determined by the Colorado River Compact, and sets forth specific terms for apportioning the use of interstate tributaries (Yampa, San Juan, Little Snake and Henry’s Fork) to the Colorado River. Additionally, the compact establishes the Upper Colorado River Commission to administers the compact and the state engineers from each Upper Basin state administer the water within their respective boundaries to achieve compliance.

Map of the Upper Colorado River Basin.
Upper Colorado River Basin. USBR (2009).

Nebraska v. Wyoming, 325 U.S. 589 (1945; modified 1953 & 2001)

Also known as the “North Platte River Decree,” this decree divides North Platte River water among Colorado, Nebraska and Wyoming. Total irrigation in Jackson County, Colorado, is limited to 145,000 acres and 17,000 acre-feet of storage for irrigation in each season. Total water exports from transbasin diversions from the North Platte River in Colorado are limited to no more than 60,000 acre-feet during any 10-year period. This decree does not affect or restrict the use or diversion of water from the North Platte River and its tributaries for ordinary and usual domestic, municipal and stock watering purposes. The North Platte Decree Committee oversees compliance and reporting under the decree and addresses disputes.

Map of the North Platte River Basin.
North Platte River Basin. Nebraska DNR (n.d.).

Wyoming v. Colorado, 353 U.S. 953 (1957)

Also known as the “Laramie River Decree,” this decree permits Colorado to divert 49,375 acre-feet of water per calendar year from the Laramie River and its tributaries, provided that Colorado diverts no more than 19,875 acre-feet per calendar year of that total amount outside of the Laramie River Basin. Colorado may also divert no more than 1,800 acre-feet after July 31 of each year for use within the basin. All waters diverted within the basin in Colorado are restricted to irrigation use, while waters diverted for use outside the basin do not have that restriction. Sand Creek is specifically excluded from the decree, and the decree is administered by the respective state engineers.

Map showing the Laramie River Basin within Colorado and Wyoming.
Laramie River Basin.

Pot Creek Memorandum of Understanding (1958; revised 2005)

Colorado and Utah believed that a compact would eventually be necessary, but in the meantime, they used a memorandum of understanding (MOU) to develop a functioning system to apportion the waters of Pot Creek. The states agreed to the appointment of a water commissioner with authority to administer in both states, and for a division of expenses, with Colorado bearing 20% and Utah 80%. Additionally, the MOU states that neither of the states can exercise direct flow diversions before May 1 of each year, and establishes a schedule of priorities for use in both states.

Sand Creek Memorandum of Agreement (1939; revised 1997)

The Sand Creek Memorandum of Agreement (MOA) allocates waters according to the priority water rights in Colorado and Wyoming, recognizing that Wyoming was entitled to 50.68 cubic feet per second before any Colorado diversions. This provision was later revised in 1997 to require Colorado to deliver 40 cfs over a seven-day period at the beginning of the irrigation season, and 35 cfs (if physically available) after that period if needed for irrigation by senior water rights holders in Wyoming. The Sand Creek MOA also limits diversions of the Sand Creek Ditch and the Wilson Supply Ditch to amounts of water in excess of the water allocated to Wyoming. The agreement is administered by the Colorado Division of Water Resources (DWR).

Convention of May 21, 1906: Equitable Distribution of the Waters of the Rio Grande 

The 1906 Convention requires that the United States deliver 60,000 acre-feet of water annually to Mexico at the International Dam at Ciudad Juarez, except during periods of extraordinary drought. Elephant Butte Reservoir in New Mexico was constructed in part to meet this obligation. The Rio Grande Compact provides that the allocations of water to the states shall not be increased or diminished by reason of changes in the delivery or loss of water to Mexico.

Utilization of the Waters of the Colorado and Tijuana Rivers, and of the Rio Grande (1944)

The 1944 treaty with Mexico guarantees delivery of 1.5 million acre-feet of Colorado River water per year to Mexico, except in times of extraordinary drought when the United States can reduce deliveries in the same proportion as the United States cuts its consumptive use. If the river does not have adequate water to meet the obligations under the treaty, the Upper and Lower Colorado River Basins must share the obligation of reducing use to make up deficiencies. The 1944 treaty also addresses Mexico’s right to Rio Grande water from Fort Quitman, Texas, to the Gulf of Mexico, and establishes the International Boundary & Water Commission (IBWC) which provides binational support and facilitates resolution of issues arising during application of U.S.-Mexico treaties on water quantity, sanitation, water quality, flood control and boundary demarcation.

Map depicting the different international water treaties and compacts between the U.S. and Mexico.
International Water Treaties Map. Nava (2015).

Colorado Division of Water Resources [DWR]. (2006). A Summary of Compacts and Litigation Governing Colorado’s Use of Interstate Streams. Denver, CO: Colorado Department of Natural Resources.

Colorado River District. (2011). Colorado River Cooperative Agreement Map [Map]. Water Supply Planning: Colorado River Cooperative Agreement.

Colorado Water Conservation Board [CWCB]. (n.d.). Interstate Compacts.

International Boundary and Water Commission [IBWC]. (2007). United States and Mexico Presentation to USGS Study Tour [PowerPoint Presentation].

Nava Jiménez, L.F. (2015). Governance of the Rio Grande/Rio Bravo watershed and the principles of sustainable development [Map]Université Laval: Quebec City, QC, Canada.

Nebraska Department of Natural Resources [DNR]. (n.d.). North Platte River Settlement [Map]. Water Planning.

Northern Water. (2018). Windy Gap Firming Project [Map]. Fact Sheet.

State of Colorado. (2015). Colorado’s Water Plan. Denver, CO: Colorado Water Conservation Board.

U.S. Army Corps of Engineers [USACE]. (2015). Memoranda of Understanding/Agreement (MOU/MOA). Natural Resources Management Gateway.

U.S. Bureau of Reclamation [USBR]. (2007). Animas-La Plata Project: Implementation of the Colorado Ute Settlement Act Amendments of 2000 [Map].

—–. (2009). Upper Colorado River Basin [Map]. Colorado River Storage Project.

U.S. Geological Survey [USGS]. (2016a). Colorado River Basin map [Map].

—–. (2016b). National Water-Quality Assessment (NAWQA) Program – South Platte River Basin [Map].

Water Education [WEco]. (2014). Citizen’s Guide to Colorado’s Transbasin Diversions. Denver, CO.

—–. (2021). Citizens’ Guide to Colorado’s Interstate Compacts (3rd Ed.). Denver, CO.