# Missouri water resource region

The Missouri water resource region is one of 21 major geographic areas, or regions, in the first level of classification used by the United States Geological Survey to divide and sub-divide the United States into successively smaller hydrologic units. These geographic areas contain either the drainage area of a major river, or the combined drainage areas of a series of rivers.
The Missouri region, which is listed with a 2-digit hydrologic unit code (HUC) of 10, has an approximate size of 520,960 square miles (1,349,300 square kilometers), and consists of 30 sub-regions, which are listed with the 4-digit HUCs 1001 through 1030.
This region includes the drainage within the United States of: (a) the Missouri River Basin, (b) the Saskatchewan River Basin, and (c) several small closed basins. Includes all of Nebraska and parts of Colorado, Iowa, Kansas, Minnesota, Missouri, Montana, North Dakota, South Dakota, and Wyoming.

## List of water resource subregions

| Subregion HUC | Subregion Name | Subregion Description | Subregion Location | Subregion Size | Subregion Map |
| 1001 | Saskatchewan subregion | The Saskatchewan River Basin within the United States. | Montana | 0,697 sq mi (1,810 km$^2$) | HUC1001 |
| 1002 | Missouri Headwaters subregion | The Headwaters of the Missouri River Basin above the confluence of and including the Gallatin, Jefferson, and Madison River Basins. | Montana and Wyoming. | 14,100 sq mi (37,000 km$^2$) | HUC1002 |
| 1003 | Missouri–Marias subregion | The Missouri River Basin below then confluence of the Gallatin, Jefferson, and Madison River Basins to and including the Marias River Basin. | Montana | 20,100 sq mi (52,000 km$^2$) | HUC1003 |
| 1004 | Missouri–Musselshell subregion | The Missouri River Basin below the confluence of the Marias River Basin to Fort Peck Dam. | Montana | 23,700 sq mi (61,000 km$^2$) | HUC1004 |
| 1005 | Milk subregion | The Milk River Basin within the United States, including the Wild Horse Lake closed basin. | Montana | 15,300 sq mi (40,000 km$^2$) | HUC1005 |
| 1006 | Missouri–Poplar subregion | The Missouri River Basin within the United States from Fort Peck Dam to the confluence with the Yellowstone River Basin. | Montana | 10,800 sq mi (28,000 km$^2$) | HUC1006 |
| 1007 | Upper Yellowstone subregion | The Yellowstone River Basin above the confluence with the Bighorn River Basin. | Montana and Wyoming. | 14,400 sq mi (37,000 km$^2$) | HUC1007 |
| 1008 | Big Horn subregion | The Big Horn River Basin. | Montana and Wyoming. | 22,800 sq mi (59,000 km$^2$) | HUC1008 |
| 1009 | Powder–Tongue subregion | The Powder and Tongue River Basins. | Montana and Wyoming. | 18,800 sq mi (49,000 km$^2$) | HUC1009 |
| 1010 | Lower Yellowstone subregion | The Yellowstone River Basin below the confluence with the Big Horn River Basin, excluding the Tongue and Powder River Basins. | Montana and North Dakota. | 14,000 sq mi (36,000 km$^2$) | HUC1010 |
| 1011 | Missouri–Little Missouri subregion | The Missouri River Basin below the confluence with the Yellowstone River Basin to Garrison Dam. | Montana, North Dakota, South Dakota, and Wyoming. | 17,300 sq mi (45,000 km$^2$) | HUC1011 |
| 1012 | Cheyenne subregion | The Cheyenne River Basin above the normal operating pool of Lake Oahe. | Montana, Nebraska, South Dakota, and Wyoming. | 24,300 sq mi (63,000 km$^2$) | HUC1012 |
| 1013 | Missouri–Oahe subregion | The Missouri River Basin from Garrison Dam to Oahe Dam, excluding the Cheyenne River Basin above the normal operating pool of Lake Oahe. | North Dakota and South Dakota. | 37,400 sq mi (97,000 km$^2$) | HUC1013 |
| 1014 | Missouri–White subregion | The Missouri River Basin from Oahe Dam to Fort Randall Dam. | Nebraska and South Dakota. | 20,200 sq mi (52,000 km$^2$) | HUC1014 |
| 1015 | Niobrara subregion | The Niobrara River Basin and the Ponca Creek Basin. | Nebraska, South Dakota, and Wyoming. | 13,900 sq mi (36,000 km$^2$) | HUC1015 |
| 1016 | James subregion | The James River Basin. | North Dakota and South Dakota. | 21,500 sq mi (56,000 km$^2$) | HUC1016 |
| 1017 | Missouri–Big Sioux subregion | The Missouri River Basin from Fort Randall Dam to and including the Big Sioux River Basin, but excluding the Ponca Creek, Niobrara River, and James River Basins. | Iowa, Minnesota, Nebraska, and South Dakota. | 13,900 sq mi (36,000 km$^2$) | HUC1017 |
| 1018 | North Platte subregion | The North Platte River Basin. | Colorado, Nebraska, and Wyoming. | 30,900 sq mi (80,000 km$^2$) | HUC1018 |
| 1019 | South Platte subregion | The South Platte River Basin. | Colorado, Nebraska, and Wyoming. | 23,900 sq mi (62,000 km$^2$) | HUC1019 |
| 1020 | Platte subregion | The Platte River Basin below the confluence of the North and South Platte River Basins, excluding the Elkhorn and Loup River Basins. | Nebraska | 8,160 sq mi (21,100 km$^2$) | HUC1020 |
| 1021 | Loup subregion | The Loup River Basin. | Nebraska | 15,000 sq mi (39,000 km$^2$) | HUC1021 |
| 1022 | Elkhorn subregion | The Elkhorn River Basin. | Nebraska | 6,950 sq mi (18,000 km$^2$) | HUC1022 |
| 1023 | Missouri–Little Sioux subregion | The Missouri River Basin below the confluence with the Big Sioux River Basin to the confluence with the Platte River Basin. | Iowa, Minnesota, and Nebraska. | 9,140 sq mi (23,700 km$^2$) | HUC1023 |
| 1024 | Missouri–Nishnabotna subregion | The Missouri River Basin below the confluence with the Platte River Basin to the confluence with the Kansas River Basin. | Iowa, Kansas, Missouri, and Nebraska. | 13,300 sq mi (34,000 km$^2$) | HUC1024 |
| 1025 | Republican subregion | The Republican River Basin. | Colorado, Kansas, and Nebraska. | 24,700 sq mi (64,000 km$^2$) | HUC1025 |
| 1026 | Smoky Hill subregion | The Smoky Hill River Basin. | Colorado and Kansas. | 19,800 sq mi (51,000 km$^2$) | HUC1026 |
| 1027 | Kansas subregion | The Kansas River Basin, excluding the Republican and Smoky Hill River Basins. | Kansas, Nebraska, and Missouri. | 15,000 sq mi (39,000 km$^2$) | HUC1027 |
| 1028 | Chariton–Grand subregion | The Chariton, Grand, and Little Chariton River Basins. | Iowa and Missouri. | 10,900 sq mi (28,000 km$^2$) | HUC1028 |
| 1029 | Gasconade–Osage subregion | The Gasconade and Osage River Basins. | Kansas and Missouri. | 18,400 sq mi (48,000 km$^2$) | HUC1029 |
| 1030 | Lower Missouri subregion | The Missouri River Basin below the confluence with the Kansas River Basin to the confluence with the Mississippi River, excluding the Chariton, Gasconade, Grand, and Osage River Basins. | Kansas and Missouri. | 10,200 sq mi (26,000 km$^2$) | HUC1030 |