The Rio Grande (/ˌriːoʊ ˈɡrænd/ or /ˌriːoʊ ˈɡrɑːndeɪ/) in the United States or the Río Bravo (del Norte) in Mexico (Spanish pronunciation: [ˈri.o ˈβɾaβo ðel ˈnoɾte]), also known as P’osoge in Tewa and Tó Ba’áadi in Navajo,[7] is one of the principal rivers (along with the Colorado River) in the Southwestern United States and in northern Mexico.

[8][9][10] The length of the Rio Grande is 1,896 miles (3,051 km), making it the 4th longest river in the United States and in North America by main stem.

[12] The Rio Grande with its fertile valley, along with its tributaries, is a vital water source for seven US and Mexican states, and flows primarily through arid and semi-arid lands.

[14] Although the river's greatest depth is 60 feet (18 m), the Rio Grande generally cannot be navigated by passenger riverboats or by cargo barges.

[15] Navigation was active during much of the 19th century,[16] with over 200 different steamboats operating between the river's mouth close to Brownsville and Rio Grande City, Texas.

They provided transport for the U.S. Army, under General Zachary Taylor, to invade Monterrey, Nuevo León, via Camargo Municipality, Tamaulipas.

Army engineers recommended that with small improvements, the river could easily be made navigable as far north as El Paso.

European warships anchored offshore to maintain the port's neutrality, and managed to do so successfully throughout that conflict, despite occasional stare-downs with blockading ships from the US Navy.

The sedimentary basins forming the modern Rio Grande Valley were not integrated into a single river system draining into the Gulf of Mexico until relatively recent geologic time.

Instead, the basins formed by the opening of the Rio Grande rift were initially bolsons, with no external drainage and a central playa.

Volcanism in the Taos Plateau reduced drainage from the San Luis Basin until a spillover event 440,000 years ago that drained Lake Alamosa, forming the Rio Grande Gorge, and fully reintegrated the San Luis Basin into the Rio Grande watershed.

[24] This led to decades of conflict (the Coalition Period), the eventual merging of cultures, and the establishment of most of the Tanoan and Keresan pueblos of the Rio Grande Valley.

The upper Rio Grande Valley was characterized by occasional periods of extreme drought, and the human inhabitants make extensive use of gridded gardens and check dams to stretch the uncertain water supply.

[25] In 1519, a Spanish naval expedition along the northeastern coast of Mexico charted the mouths of several rivers including the Rio Grande.

In the autumn of 1540, a military expedition of the Viceroyalty of New Spain led by Francisco Vásquez de Coronado, Governor of Nueva Galicia, reached the Tiwa pueblos along the Rio Grande in the future New Mexico.

The project also accorded 60,000 acre-feet (74 million cubic meters) of water annually to Mexico in response to the country's demands.

This act was the first occurrence of congressionally directed allocation of an interstate river (although New Mexico would not achieve statehood till 1912).

With negotiations remaining stagnant, Texas sued New Mexico over the issue in 1935, prompting the intervention of the president who set up the Rio Grande Joint Investigation the findings of which helped lead to the final agreement.

In mid-2001, a 328-foot (100 m)-wide sandbar formed at the mouth of the river, marking the first time in recorded history that the Rio Grande failed to empty into the Gulf of Mexico.

For much of the time since water rights were introduced in the 1890s, the Rio Grande flowed through Las Cruces from February to October each year, but this is subject to climate change.

[33] As of January 2021, the Elephant Butte Irrigation District (Ebid) expected that water shortages would mean the river only flows through Las Cruces from June through July.

[33] The water shortages are affecting the local ecosystem and endangering species including cottonwood trees and the southwestern willow flycatcher.

"[35] In response, New Mexico increased its program offering to subsidize farmers who fallow their fields rather than planting crops, which uses additional water;[36] the city of Albuquerque shut off its domestic supply diversion and switched to full groundwater pumping in 2021.

[37] Additionally, in 2022, work began on El Vado Dam, during which it is unavailable for storage, reducing system capacity by about 180,000 acre-feet.

[42][43] By that summer, after the spring runoff had concluded and due to a failed New Mexico monsoon season and record high temperatures, the river went dry in Albuquerque for a second consecutive year.

Use of that water belonging to the United States is regulated by the Rio Grande Compact, an interstate pact between Colorado, New Mexico, and Texas.

Diversions are restricted during periods of low river flow in order to protect the riparian ecosystem and mitigate effects on endangered species like the Rio Grande silvery minnow.

Diversions, mainly for agricultural irrigation, have increased the natural decrease in flow such that by the time the river reaches Presidio, little or no water is left.

Large diversions for irrigation below Rio Grande City reduce the river's average flow to 889 cubic feet per second (25 m3/s) at Brownsville and Matamoros.

By the late 19th century, in the United States, the name Rio Grande had become standard in being applied to the entire river, from Colorado to the sea.