Tim Fitzharris / River in gorge, Rio Grande Gorge, Rio Grande del Norte National Monument, New Mexico

Jack Dykinga / Rio Grande passing through the towering cliffs of the Mariscal Canyon, Texas, USA

Jack Dykinga / Aerial view of Rio Grande passing through the Boquillas Canyon with the Chisos Mountains and Big Bend National Park in the background, Texas, USA on right of river, Mexico on left of river.

Tim Fitzharris / Sierra Ponce and Rio Grande, Big Bend National Park, Texas

Jack Dykinga / Dawn light on Santa Elena Canyon with Rio Grande River, Big Bend National Park, Chihuahuan Desert, Texas, USA, February.

Tim Fitzharris / Cottonwood (Populus sp) trees along the Rio Grande in autumn, Wild Rivers Recreation Area, New Mexico

Tim Fitzharris / River in gorge, Rio Grande Gorge, Rio Grande del Norte National Monument, New Mexico

Tim Fitzharris / River in gorge, Rio Grande Gorge, Rio Grande del Norte National Monument, New Mexico

Tim Fitzharris / Sunset over Rio Grande gorge at Sheep Crossing, Rio Grande del Norte National Monument, New Mexico

Tim Fitzharris / Rio Grande Wild and Scenic River, Rio Grande del Norte National Monument, New Mexico

Tim Fitzharris / Rio Grande Wild and Scenic River, view from Sheep Crossing to Ute Mountain, Rio Grande del Norte National Monument, New Mexico

Tim Fitzharris / Sunrise at Rio Grande Wild and Scenic River, Rio Grande del Norte National Monumnet,south of Taos, New Mexico

Tim Fitzharris / Rio Grande Wild and Scenic River,view from Sheep Crossing to Ute Mountain, Rio Grande del Norte National Monument, New Mexico

Tim Fitzharris / Common Cattail (Typha latifolia) along the Rio Grande, Rio Grande del Norte National Monument, New Mexico

Tim Fitzharris / River valley, Rio Grande, Rio Grande del Norte National Monument, New Mexico

Jeff Foott / Cactus and Rio Grande, Big Bend National Park, Texas

Jeff Foott / River at dawn, Rio Grande, Big Bend National Park, Texas

Charlie Summers / Red-tailed hawk (Buteo jamaicensis) gliding above the Rio Grande River, Bosque del Apache, New Mexico, USA, December.

Christian Ziegler / Red Mangrove (Rhizophora mangle) aerial roots, Rio Grande, southern Belize

Christian Ziegler / Red Mangrove (Rhizophora mangle) aerial roots, Rio Grande, southern Belize

Christian Ziegler / Orchid (Caularthron sp) epiphytes on the trunk of a Black Mangrove (Avicennia germinans), Rio Grande, southern Belize

Christian Ziegler / Red Mangrove (Rhizophora mangle) aerial roots, Rio Grande, southern Belize

Christian Ziegler / Bromeliad (Tillandsia sp) flower in mangrove forest, Rio Grande, southern Belize

Christian Ziegler / Red Mangrove (Rhizophora mangle) aerial roots, Rio Grande, southern Belize

Luciano Candisani / Fig (Ficus sp) tree and Rio Grande Waterfall, Brazil

Patricio Robles Gil / Rio Grande flowing through arid landscape in the Sierra del Carmen region, Mexico

Patricio Robles Gil / Rio Grande flowing through arid landscape in the Sierra del Carmen region, Mexico

Patricio Robles Gil / Ocotillo (Fouquieria splendens) growing along the Rio Grande River, Sierra del Carmen region, Mexico

Patricio Robles Gil / Mountains of Sierra del Carmen tower 5,000 over the desert floor and the Rio Grande, eastern Sierra Madre Range, Mexico

Patricio Robles Gil / Rio Grande running through arid landscape of the Sierra del Carmen region, Mexico

Tim Fitzharris / Rio Grande, Big Bend Ranch State Park, Chihuahuan Desert, Texas

Tim Fitzharris / Rio Grande winding through Madera Canyon, Big Bend Ranch State Park, Chihuahuan Desert, Texas

Tim Fitzharris / Rio Grande from Big Hill Overlook, Big Bend Ranch State Park, Chihuahuan Desert, Texas

George McCarthy / People canoeing on Rio Grande river, Boquillas Canyon, Big Bend National Park, Texas, USA

Philippe Clement / Cloud forest and river at Rio Grande de Orosi, Tapanti NP, Costa Rica

Tim Fitzharris / Rio Grande and Sangre de Cristo Mountains, Colorado

Mike Wilkes / Looking out over the Rio Grande River, Texas, USA

Tim Fitzharris / Rio Grande and the Sangre de Cristo Mountains, Colorado

Tim Fitzharris / Rio Grande and the Sangre de Cristo Mountains, Colorado

Tom Vezo / Green Jay (Cyanocorax yncas) perching, Rio Grande River Valley, Texas

Gerry Ellis / Lowland chaparral in the Rio Grande River Valley, Bosque del Apache National Wildlife Refuge, New Mexico

Gerry Ellis / Lowland chaparral in the Rio Grande River Valley, Bosque del Apache National Wildlife Refuge, New Mexico

Tim Fitzharris / Rio Grande and limestone cliffs of the Sierra Ponce, also known as Mesa de Anguilla, Big Bend National Park, Texas

Tim Fitzharris / River in gorge, Rio Grande Gorge, Rio Grande del Norte National Monument, New Mexico

Tim Fitzharris / Rio Chama, tributary of the Rio Grande near Abiquiu, New Mexico

Christian Ziegler / Red Mangrove (Rhizophora mangle) aerial roots, Rio Grande, southern Belize

Christian Ziegler / Red Mangrove (Rhizophora mangle) growing along Rio Grande, southern Belize

Christian Ziegler / Red Mangrove (Rhizophora mangle) aerial roots, Rio Grande, southern Belize

Christian Ziegler / Orchid (Caularthron sp) epiphytes on the trunk of a Black Mangrove (Avicennia germinans), Rio Grande, southern Belize

Christian Ziegler / Red Mangrove (Rhizophora mangle) forest along Rio Grande, southern Belize

Christian Ziegler / Red Mangrove (Rhizophora mangle) forest, Rio Grande, southern Belize

Patricio Robles Gil / Ocotillo (Fouquieria splendens) cactus along the Rio Grande, Big Bend National Park in the Chihuahuan Desert, Texas

Tim Fitzharris / Rio Grande Gorge near Taos, New Mexico

Gerry Ellis / Lowland chaparral in the Rio Grande River Valley, Bosque del Apache National Wildlife Refuge, New Mexico

Wendy Shattil / Aerial view of Rio Grande and border crossing between Roma, Texas, USA and Ciudad Miguel Aleman, Tamaulipas, Mexico. July 2019.

Wendy Shattil / Lower Rio Grande Valley between Roma and Rio Grande City, Texas, USA. Aerial view from Tamaulipas, Mexico. July 2019.

Wendy Shattil / Aerial view of border wall at Southmost Preserve, Texas, USA. 85% of the reserve lies on the no-man's land side between the wall and the Rio Grande river disrupting The Nature Conservancy's ac...

Wendy Shattil / Aerial view of Lower Rio Grande Valley and coast north of Rio Grande river to South Padre Island, Cameron County, Texas, USA. July 2019.

Wendy Shattil / Aerial view of Rio Grande flowing into Gulf of Mexico, the border between Cameron County, Texas, USA and Tamaulipas, Mexico. July 2019.

Wendy Shattil / Aerial view of Rio Grande flowing into Gulf of Mexico, the border between Cameron County, Texas, USA and Tamaulipas, Mexico. July 2019.

Wendy Shattil / Aerial view across Las Palomas Wildlife Management Area, Cameron County, Texas, USA to mouth of the Rio Grande and Gulf of Mexico. River is border with Tamaulipas, Mexico. July 2019.

Wendy Shattil / Aerial view of the Rio Grande near its mouth, the border between Tamaulipas, Mexico and Cameron County, Texas, USA. July 2019.

Wendy Shattil / Aerial view of Madero looking across the Rio Grande to Ejido Los Cavazos Tamaulipas, Mexico. Hidalgo County, Texas, USA. July 2019.

Wendy Shattil / Meanders of the Rio Grande with view towards Tamaulipas, Mexico from Bensen-Rio Grande State Park, aerial view. Illustrates challenge of building a border wall alongside the river. Mission, Texas, USA...

Wendy Shattil / View from La Joya across Walker Lake to Las Palomas Wildlife Mangement Area, Rio Grande and Tamaulipas, Mexico beyond. Hidalgo County, Texas, USA. July 2019.

Wendy Shattil / Rio Grande, the border between Tamaulipas, Mexico and USA. Border wall on USA side of river, aerial view. Lower Rio Grande, Texas, USA. July 2019.

Wendy Shattil / Aerial view of border crossing over Rio Grande towards Tamaulipas, Mexico. Border wall in Hidalgo County, Texas, USA. July 2019.

Wendy Shattil / Aerial view of Rio Grande, the USA-Mexico border. Near Roma, Starr County, Texas, USA. July 2019.

Wendy Shattil / View across Rio Grande to Tamaulipas, Mexico. Santa Ana National Wildlife Refuge, near Alamo, Hidalgo County, Texas, USA. July 2019.