Austin myth busted (sort of): The truth about Barton Springs temp

1:16 p.m Tuesday, July 18, 2017 Lifestyle

A jump into Barton Springs Pool raises goosebumps and turns lips blue. That’s what 68-degree year-round water does to a body, right?

Not so fast.

Despite T-shirts that proclaim it, websites that tout it and a Wikipedia entry that boasts it, the water temperature at Barton Springs isn’t 68 degrees, and rarely has it been.

We headed to the pool recently with David Johns, a hydrogeologist for the City of Austin, and his assistant, Walker Stone, to dunk a multi-sensor probe into three locations at the spring-fed swimming pool and let science do the talking.

A swimmer floats on the water surface at Barton Springs Pool on July 12. You don’t need to know the official temperature to enjoy the warmth of the sun and the cool of Barton Springs on a hot summer day. NICK WAGNER/AMERICAN-STATESMAN

Our results? At the fault line next to the diving well, near the main spring, the temperature read 70.6 degrees. But at the surface by the downstream dam, it was 71.6 degrees. It was even warmer at the shallow end of the pool, where it measured 74.9 degrees.

Myth busted, then? Sort of.

The pool has, at times, measured 68 degrees. But it’s not all that common, and certainly not during the summer, when most people are taking that polar bear plunge. The temperature varies slightly, depending on time of year and discharge volume. Mostly, it depends on what season rains fall.

Barton Springs is fed by a karst aquifer, and rain that falls in its recharge zone moves rapidly to the springs. When it rains during the winter, water entering the aquifer is already chilly — about 50 or 55 degrees — making the water that emerges from the springs cooler. If rain falls and creeks flow in the summer, the water soaks in at a much warmer temperature, and the spring’s flow is warmer.

Walker Stone, an intern with the city of Austin Watershed Protection Department, tests the water temperature at Barton Springs Pool on July 12. The average temperature across three points in the pool this day was 72.4 degrees. NICK WAGNER/AMERICAN-STATESMAN

For years, the City of Austin website stated that the pool’s water temperature hovered around 68 degrees year-round. Today the website claims an “average temp of 68 to 70.” That’s still not quite accurate, but closer than the Wikipedia entry for the pool, which boldly states, “The pool is a popular venue for year-round swimming, as its temperature maintains a stable 68 °F (20 °C) in the winter and summer.”

“I was talking to someone just the other day who said it was 68 degrees. I had to bite my tongue. It’s an urban myth,” said Johns, ever the scientist.

Need more evidence? Sensors in an opening at the bottom of the pool near the main springs that are now monitored by the USGS have automatically taken a temperature reading every 15 minutes since 1993. That’s typically the coolest spot in the pool during the summer, and the temperature there has held a consistent 70.5 degrees for the past few weeks. It hasn’t dropped below 70 since April.

“Some people say it seems colder than that, but it’s still 30 degrees colder than body temperature, so it’s cold,” Johns says.

David Johns, a hydrologist with the city of Austin Watershed Protection Department, holds onto a device that tests water temperature while Walker Stone, an intern with the department, untangles the cord at Barton Springs Pool on July 12. NICK WAGNER/AMERICAN-STATESMAN

Nobody really knows how that 68-degree myth got started. Maybe the temperature actually did measure 68 one day when someone took a reading. It wasn’t steady, though, and it wasn’t year-round. Johns suspects someone at the city settled on 68 for nothing other than it sounded good. “Sixty-eight sounded cooler and more hip than 70,” he said.

As Johns prowled Barton Springs on our visit, more than a few swimmers howled as they submerged themselves in chilly water. Renee Epstein shivered as she waded out of the shallow end.

“It’s very cold,” Epstein said. “My guess is 58 degrees.”

John Longoria and Rob Borromeo pegged it at a little warmer, somewhere between 65 and 68, then cannonballed into the pool. When they heard what Johns’ temperature probe read, they laughed.

“Check your instruments!” Longoria shouted from the water.

If you still get goosebumps when you leap in, don’t worry. You’re not alone.

“For you and me, it’s still bracing,” Johns says.

Walker Stone, an intern with the city of Austin Watershed Protection Department, tests the water temperature as Alex Schmandt, of Washington, D.C., watches at Barton Springs Pool on July 12. Ask around the pool and you’ll get a variety of answers to “What do you think the water temperature is?” NICK WAGNER/AMERICAN-STATESMAN
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