How is Austin’s Big Stacy Pool naturally heated?

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You know how Barton Springs Pool is 70 degrees year-round and naturally fed from underground springs? Well, think of Big Stacy Pool as the same thing, except hot.

But how?

That’s what Texas Parks and Wildlife botanist Anna Strong wanted to know when she posed the question back in October. What she didn’t know when she asked was that the swimming hole’s natural heating is at risk.

Big Stacy is nestled in the Travis Heights neighborhood, less than a mile from Travis Heights Elementary School. The six-lane pool is open every day except Mondays and when the temperature outside is below freezing. It’s 90-100 degrees year-round, ideal for winter swimming. About 50 swimmers visit each day in the winter months.

The history of the pool

Big Stacy Pool opened its doors in 1937 after the city added “Big” to its name to distinguish it from the nearby Little Stacy Wading Pool. The name “Stacy” comes from Gen. William Stacy, a Spanish-American War veteran and real estate agent who developed Travis Heights.

Sarah Marshall, program coordinator for historic preservation at Austin Parks and Recreation, said the pool was paid for with New Deal money under President Franklin D. Roosevelt’s Works Progress Administration.

“Travis Heights and Fairview Park are listed as historic districts to the National Register of Historic Places,” Marshall said. “The pool and its bathhouses and the seawall are actually contributing to the historical significance of the entire district.”

She said the pool’s natural heating system plays a role in its historic preservation and is a major draw for visitors — both today and in the ’30s. Marshall notes the pool back then was constantly packed.

Another thing that keeps people coming back is that the pool is free.

“We have to pay for a lot of things,” Strong said, “but … having a free pool where you can swim laps or you can splash around … is something that we just don’t experience all that often anymore.”

Capturing the earth’s warmth

The pool is surrounded by bathhouses, benches and a shed where lifeguards and staff sit during breaks. What many folks don’t see is the door behind the pool leading to what appears to be just a hole. Paul Slutes, manager of the city of Austin’s Aquatic Division, knows it as the entrance to a geothermal well.

The well is drilled deep into the earth to capture warm water from beneath the surface. This water moves through pipes that filter and transfer it to the pool.

The system was established back when the pool first opened, but Slutes said one thing has changed.

“That pool just used to use freshwater coming in — whether it was well water or city water — and it would flow into the gutters and flow out to the creek,” he said. “And sometime in 1996, we rebuilt it and made it a circulation system as we did many of the pools in Austin about that time.”

To harness as much heat as the pool does, the well is dug deep into the earth – 1,600 feet deep.

“The well won’t come on this time of year during the summer because the water is already so warm, that it won’t call for heat,” Slutes said. It doesn’t run when the temperature outside is above 80.

In that sense, Texas heat is its own natural heating system — which Austinites are already familiar with.

Time takes a toll

Beverly Deutsch has been an avid swimmer at Big Stacy for as long as she can remember. In 2021, she had a stroke and the pool played a paramount role in her recovery.

“I use it to do my laps for my ongoing physical therapy recovery from stroke because I had lost my right side function and the ability to speak,” she said. “You never completely recover, but swimming here helps.”

For many pool-goers like Deutsch and Strong, the natural warmth of Big Stacy is essential. However, that natural heat may not be around for much longer. The well that feeds warmth to the pool has become weak.

Slutes said five or six years ago the city’s aquatic division and well experts tried to clean it using high-frequency sound for the first time. They realized time had taken a toll on the well and because of how fragile its casing had become, cleaning it could make the entire well collapse on itself.

“A few years ago, we actually installed a couple of heaters as a backup,” Slutes said. “So we do have heaters now plumbed in, ready to go in case the well does fail.”

While the new heaters are tested annually, they have not been put to use just yet. When they become fully operational, Big Stacy Pool will no longer be naturally heated. The resulting gas bill won’t be cheap.

“We’ve paid up to $10,000 a month to heat a pool,” Slutes said. “[The natural heating] does save us like a gas bill that we would have to incur and that can be very expensive for swimming pools, especially a swimming pool that size.”

He said well experts advised the city to leave the deteriorating well alone. For now, repairs are not an option, but installing a new well is something the city could consider.

So the city has a Plan B: those backup heaters.

Strong said she is grateful, because she doesn’t want Austin to lose this warm pool.

“That means that they’re preparing for the future, which is good,” she said. “But I guess they want to continue having this pool as a year-round pool and the temperature is part of it.”

This is a testament to the community’s commitment to preserving a piece of Old Austin, she said, a place where natural wonders and the swimming hole dubbed Big Stacy Pool unite generations.

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