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Greener pastures grow under water in the Pantanal de Mato Grosso do Sul, an immense area of wetlands in western Brazil.

On his feet hours before sunrise, 66-year-old Joao Aquino Pereira readies the horses and wakes up the herd of oxen for a new day in the three-week pilgrimage in search of grass to graze.

"Today's going to be one of those days," says the old cowboy, forecasting the weather by looking up at the red skies. "It seems like it'll be a hot one and we still need to prepare the cattle to go across the river."

The crossing of the Taquari River requires all the skill Pereira has amassed in decades of experience. Along with five other mounted cowboys, he'll have to line up and guide 520 oxen through the depths of the overflowing river. Each day, the men and animals traverse about 11 miles (18 kilometers), from dawn until 3 p.m., in temperatures averaging about 90 degrees Fahrenheit (32 Celsius) during the day. At different moments during the trip, the men cross paths with macaws, deer and pit vipers, all seemingly unfazed by their presence.

Dressed with leather chaps on top of their jeans, Stetson hats and machetes attached to their waists, before setting off the men finish their breakfast with terere, a yerba mate tea served ice cold from a cup made out of an ox horn.

Working as a cowboy is still a way of life in rural areas of Latin America's largest nation. While ranchers on the coasts can transport cattle with trucks, the excess of water and the shortage of roads make that impossible in the biggest floodplain in the world.

Ranchers here contract out the grazing business, and being a cowboy is reasonably well-paying for the region. Cowboys earn an average of $18 dollars a day, and the leader of the group can earn as much as $285 per day.

Rene de Almeida, 70, has been leading groups since he was 25.

"It's better to guide the herd when it's raining," he explains, adding that once he led a group for 97 days straight. "During droughts, the land is too hot and the oxen get tired and thirsty."