This is a passenger announcement. You can now book your train on Uber and get 10% back in credits to spend on Uber eats.

So you can order your own fries instead of eating everyone else's.

Trains, now on Uber. T's and C's apply. Check the Uber app.

This is Sign- 62nd Science. I'm Jason Goldman.

In the 1800s, many rivers in the American West were diverted for irrigation or damned for generating electricity.

So rapidly expanding cities began tapping into groundwater.

Add climate change into the mix,

and you can see how an already arid desert

can become even more parched.

The banks of the Santa Cruz River in southeastern Arizona were described in 1855 as covered with

poplars and willows, ash trees and plantains, oaks and walnut trees. But a century later, the river was gone.

But it was the original river of Tucson and the reason the city is here.

Ecologist Michael Bogan from the University of Arizona.

70 years after it ran dry, the city of Tucson decided to release treated wastewater back into the riverbed,

around 2.8 million gallons each day.

Bogan went to participate in the festivities when the valves were opened in June 2019.

And everybody was splashing around in the water and excited to see water back in the river. And what I immediately got sidetracked with was the number of dragonflies that I was seeing. Within a few hours, Bogan counted seven different species of dragonflies.

He even saw dragonflies and damselfly mating and laying eggs at a river that had not existed earlier that day.

And so I was like, oh my gosh, I need to study this.

This is so cool that these species are coming back so fast.

Just three months later, Bogan's team had documented roughly the same abundance and diversity

of dragonflies that they'd seen in other parts of the river that have been flowing for years. Also abundant were may flies and catus flies.

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