For many Big Bend National Park regulars, it's an essential stop after a day of desert adventuring. To ease into the soothing waters of the park's hot springs, near Rio Grande Village, is pure animal satisfaction. Indeed, these springs were one of the region's first tourist attractions.

But the park's thermal springs – there are many – conceal a wonder most blissful soakers never guess at. The Big Bend gambusia is found only in a few warm pools in the park. The lovely, 2-inch fish has escaped brushes with extinction time and again. It's a small creature – with an epic story.

Dr. Sean Graham, of Sul Ross State University in Alpine, monitors the Big Bend gambusia.

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