(Photo by Annika Cline - KJZZ) The Sierra Estrella mountain range peeks over wetland grasses. (Photo by Annika Cline - KJZZ) Researchers from Arizona State University gather data on wetland plants.

The Tres Rios Wetlands project was completed by the city of Phoenix in 2010. An area once patched with farm fields was turned into a network of waterways and greenery. It’s grown since then. Pay a visit today and it’s clear the wetland has taken on a life of its own.

In a chorus of birds, it’s hard to pick out a single voice. Unless you’re a birder who’s been listening to this song for many years.

“This is a common yellowthroat which I hear singing right now,” said Mark Larson, one of those savvy birders.

“This is a species that’s tied to wetlands,” he said. “So it would be otherwise rare in the desert, as you can imagine.”

The Tres Rios Wetlands is a man-made oasis in southwest Phoenix, next to the Salt River. Larson said it’s one of the best birding sites in the state.

“One time I came here and I saw a species of bird that normally is not in the state of Arizona at all, and it’s called a painted bunting,” Larson said.

What the painted bunting doesn’t know is this wetland wasn’t made for it or the other critters that live here - not for the beavers or bullfrogs or the hundreds of other birds. It was made to treat the wastewater of all the people who live outside it.

“I’ve been doing Tres Rio Wetlands now for almost 20 years,” said Ron Elkins.

Elkins is with the City of Phoenix’s water department, and he’s seen the wetlands grow from a small research project, to the full-sized wetlands that now stretch from 91st Avenue to 115th. It’s a web of water and plants so dense you can’t see the desert beyond. And it’s a cost-effective way to treat water.

“What would cost several billion dollars to do with concrete and steel, has cost you a minimal level - down in the millions - to do it naturally,” Elkins said.

It’s also unconventional.

“One thing that’s true in a wetlands: two plus two does not equal four. And it is not about, you got this much water coming in and that much water coming out,” he said.

The team at first was just focused on the water. Some early mistakes taught them to see the bigger picture, like when swaths of algae attempted to smother the lakes. They realized they needed to foster an environment where the algae and the bacteria were balanced.

“We thought it would be, you turn this knob, it does this, you push that button. It’s not like that at all,” Elkins said.

Now the wetlands area is more mature, they mostly step back and let it do its thing. Since then, Elkins has seen some pretty incredible wildlife just show up.

“We noticed within the first year or two that we were starting to get some different populations of fish,” Elkins said.

Fish that somehow made it through the various barriers the department set up. That sure made the pelicans happy, though.

“American white pelicans have been wintering here,” said Mark Larson. “They breed in the upper midwest on prairie ponds.”

Larson said it’s not unusual for these snowbirds to winter in Arizona. “But there now are a few that actually stay here all year.”

“That is unprecedented,” he added.

There are also a lot of people flocking in: researchers, students and nature enthusiasts. The city has documented visitors from 23 states and Canada. So, the department is turning its attention toward growing the recreational side of the wetlands. Their next step is to connect the Tres Rios trail with the Maricopa Trail, and promote this as a place for anyone to stop by and discover something new.