Beneath the calm, spring-fed headwaters in the Barrens Plateau, a bitter battle is being fought.
A hungry horde is gobbling up resources, and invaded natives are struggling for survival.
Even bigger fish can't get too comfortable in these small ponds.
Few species learned that lesson better than the Barrens topminnow.
Once, the colorful, 4-inch fish thrived in ponds throughout the Barrens Plateau region of Middle Tennessee, according to Matt Hamilton, senior aquarist at the Tennessee Aquarium.
The topminnow led a peaceful life, eating insects, larvae and freshwater plankton.
But then the horde came.
"In the 1800s, people started bringing the western mosquitofish, which is native to West Tennessee but not here, into these sites for their reputation for mosquito control," Hamilton said.
The smaller, invasive mosquitofish were many, and they were good at their jobs -- too good.
First they ate the topminnows' food source, mosquito larvae, then the topminnows' own hatchlings.
"They eat the topminnows' larvae, which lessens recruitment. So the chain stops," Hamilton said.
If these topminnows die out, there is not much hope for the species. Like many species in Tennessee, the Barrens Plateau is the only place on the planet where these topminnows exist in the wild.
That's why Hamilton, along with Brad Bingham, a state coordinator for the U.S. Fish & Wildlife Service, spent most of Thursday wading into Summitville Springs, in Coffee County, working to bolster the topminnow's forces.
Their joint efforts were part of a topminnow repopulation program led by the aquarium and funded in part through U.S. Fish & Wildlife and other conservation programs.
The goal of the program is simple: Keep the Barrens topminnow off the federal endangered species list.
"The state lists the species as endangered. Part of the project is to reproduce this species in captivity and release them back into the wild," Hamilton said. "We're trying to see if we could recover the species before we had to go to the federal endangered species [listing]."
This week, Hamilton and Bingham released some adult topminnows into one of three sites and collected fish from another site to breed at the aquarium.
Bingham said the project will be successful,if topminnow populations can return and sustain themselves in 15 historic sites throughout the six-county Barrens Plateau region, which includes Grundy, Franklin, Coffee, Cannon, Warren and Dekalb counties.
A key to the program's success so far has been working with residents of the plateau, Bingham said.
"The species occurs almost exclusively on private property. We've had a lot of good relationships with the property owners," he said.
Contact staff writer Louie Brogdon at 423-757-6481 or email@example.com. Follow him on Twitter at @glbrogdoniv.