TWIN FALLS • In a lovely, little-known spot, a new urban fishery offers bass and bluegill to anglers willing to hike or bike a mile of trail. But they don’t even have to drive out of town to get there.
 
Never heard of such a pond? You’re not alone.
 
This is Bluegill Lake, a 3-acre pond in the city’s Auger Falls Heritage Park, a nonmotorized expanse inside the Snake River Canyon at the city’s north end.
 
Accessible by mountain bike trails, Bluegill Lake holds agricultural wastewater from canals that spill over the canyon rim. Bunches of yellow wild irises bloom at the water’s edge. Beyond the lush vegetation of the banks, the canyon walls provide a dramatic backdrop. Make the walk to the lake, and you’re likely to meet great blue herons, red-winged blackbirds, Canada geese and a selection of ducks.
 
And under the surface swim the bluegill and largemouth bass populations that the Idaho Department of Fish and Game stocked here in 2013. The two species — a classic pairing — thrive in the warmer water of irrigation returns, the broken shoreline, the shallow water, the aquatic vegetation.
 
“They’re phenomenal table fare,” said Scott Stanton, Fish and Game’s regional fisheries biologist.
 
What’s missing? Families with fishing poles.
 
“I have not seen anybody fishing down here yet,” Stanton said.
 
Neither has Twin Falls Parks and Recreation Director Wendy Davis.
 
Fish and Game wants to spread the word about Bluegill Lake, where fishing is open year-round, the state’s general rules apply and the whole bank is good habitat for fishing.
 
But Stanton also wants anglers to know about this pond because harvest is the best management tool he has to push up the size structure within the fish populations.
 
Largemouth bass and bluegill prey on each other’s young. If either species is too numerous, too few of the other species survive and the dominant fish population becomes overcrowded and stunted.
 
• • •
 
To know whether Bluegill Lake’s fishery is successfully established, Stanton needs to see the relative numbers of bass and bluegill, and the sizes within those populations.
 
A strange contraption is his tool for sampling that underwater world: a drift boat carrying a generator, a power converter and a pair of big metal “spiders” on poles.
 
It sounds like an electrical circuit because it is — a circuit designed for nonlethal electrofishing. The two spiders, submerged and dangling their metal tentacles underwater, are the anodes. The metal boat is the cathode. The setup sends current through the water, temporarily stunning the nearby fish.
 
On May 5, Stanton rowed the boat along Bluegill Lake’s shoreline, closing the electrical circuit with a foot pedal. He adjusted the system to deliver a charge that would — in water of this particular conductivity — efficiently collect a big sample while minimizing the time the fish would be impaired.
 
If Stanton’s job was science that morning, Anna Medina’s was plain hard work.
 
The fisheries technician stood in the bow with a long-handled net, working rapidly to scoop up stunned fish as they floated up.
 
“Stay on it!” Stanton yelled over the generator’s racket.
 
Medina quickly flipped each fish into the boat’s live well — a plastic garbage can equipped with an oxygen tank and half filled with lake water. Amazingly deft, she maneuvered to avoid whacking the handle of her net into the onlooker who shared the bow.
 
“I’ve seen people get flattened,” Stanton said later. “Myself included.”
 
Anyone on this boat wears rubber gloves and rubber boots, and the converter at Stanton’s elbow has a big red button — the “dead-man switch” — for shutting down everything in an emergency.
 
• • •
 
On the bank, Stanton and Medina set up a simple field lab on their truck tailgate: a measuring board and a scale.
 
Medina scooped some of the fish from the live well into a bucket, and Stanton worked through them quickly, announcing lengths and weights in millimeters and grams as Medina took notes.
 
One stunned bluegill burped up a young-of-the-year bluegill, and Stanton showed off the tiny fish in his palm.
 
“It suggests, yes, we are getting some recruitment,” he said. “They are spawning.”
 
Stanton laid one bluegill and one bass on the measuring board and took a photo with his phone.
 
“See how they’re the same size?” he said. “That’s a pretty good indication that we have too many fish.”
 
Nobody, it suggests, has enough food to grow big.
 
In the first half of the May 5 sampling, numbers of bass and bluegill were about even.
 
“But what we’re not seeing is different sizes, which is a little concerning,” Stanton said.
 
That tailgate analysis was preliminary, however. The team still had a second 10-minute electrofishing session to complete that day. It’s possible that by early May larger fish hadn’t yet moved into the shallower water — where the team was sampling — to spawn. And, by some researchers’ estimates, electrofishing samples only about 15 percent of the population.
 
“But with any type of science it gives us an idea,” Stanton said. “We can develop trends.”
 
All the fish went back in the lake except two bullhead catfish; apparently, they found their way into the lake with the canal water. These two would never wake up.
 
Stanton that day was watching for a more nefarious intruder, one that has wrecked fisheries elsewhere in southern Idaho.
 
“I didn’t see any carp, thankfully.”