When Gregg Eckhardt pitched the idea of cleaning up the banks of Mitchell Lake with manmade wetlands more than two-and-a-half decades ago, he wasn’t sure he’d ever see the project actually take off.

The formerly very stinky site on the South Side between Texas A&M University-San Antonio and the Mission del Lago golf course was once a spot where the City of San Antonio stored raw sewage, then later partly treated sewage to use in irrigation.

Although new sewage ceased being added to the lake in the 1980s, residual sludge caused blooms of algae to grow and change the water’s pH levels. Because of this, anytime water overflowed the banks, SAWS was in violation of the wastewater treatment plant permit it secured for the lake in 1974.

In 2016, the U.S. Environmental Protection Agency issued an administrative order calling on SAWS to develop a plan to address the periodic overflow. It was then that Eckhardt, a senior analyst with production and treatment operations at SAWS, again brought up the idea of manmade wetlands to his administrative peers at SAWS. The wetlands would act as a filter, cleaning escaped water before it reached the nearby Medina River, Eckhardt explained.

Now, six years later, SAWS has deemed its 1-acre pilot successful and is readying to scale up the man-made wetland across up to 100 acres on Mitchell Lake’s southern banks. It’s a dream come true for Eckhardt and his partner on the project, Dan Crowley, director of governmental relations at SAWS.

“Pardon the pun, but it’s a green solution to a green problem,” Crowley said with a grin.

How did we get here?

Driving to Mitchell Lake today, one must first pass under a large iron gate that reads ”Mitchell Lake wetlands” onto a white dirt road. The large blue lagoon is surrounded by cattails and tall brush. Dozens of wooden stumps protrude from the water, birds perched on several.

While rumor has it that Mitchell Lake is one of the only two natural lakes in Texas, the thousands-of-years-old body of water was likely not much of a lake at all by the time it was found by explorers in the 1700s, Eckhardt explained on a recent tour of the pilot wetland. Named by early Spanish settlers the Laguna de los Patos, or Duck Lagoon, it is described in historic journals as wadable and was likely closer to natural wetlands, Eckhardt said.

In 1839, Asa Mitchell purchased 14,000 acres in what is now southern San Antonio that included what would become known as Mitchell Lake. It soon became a popular spot for birding and duck hunting; protruding stumps and stalks standing in the lake today still mark many former duck blinds.

That all changed, however, after the city bought the lake in 1901, building a dam and then directing raw sewage into the lake.

“Legend is that the dam was built out of rubble from a flood in downtown San Antonio, around the turn of the century,” Eckhardt said. “If you walk out on the dam today, you do find pieces of bathroom tiles and such.”

By 1971, the area had become so smelly and the lake so overloaded with organic material that local residents filed lawsuits against the city. The complaints made their way to the Texas Legislature, where state government officials got involved.

“They decreed that there would be a report prepared about what to do with Mitchell Lake … a plan for remediation,” Eckhardt said. “So in 1974, Mitchell Lake got permitted as a wastewater treatment plant.”

A year earlier, the city declared the lake a refuge for waterfowl and shore birds, but with the wastewater permit, the city still used the lake for sewage discharge until 1987. SAWS assumed responsibility for the 600-acre lake in 1992.

While SAWS was able to better regulate and treat the lake under a wastewater permit and later, in 2020, a stormwater permit, the lake’s pH levels still varied greatly due to the algae.

After the EPA issued its administrative order over the permit violations, SAWS commissioned a study weighing various solutions.

Eckhardt said SAWS wanted to address this issue in the greenest way possible, as despite the algae, the lake had evolved into a paradise for birds. Located along the Central Flyway migratory path, bird aficionados have logged more than 300 species at the site. The lake has also become home to a bird sanctuary, Mitchell Lake Audubon Center, where eco-tourists come from all around the world to visit. SAWS didn’t want to drastically alter these birds’ environment, Eckhardt said.

“So what we proposed to the EPA was a constructed wetland below the lake,” he said. “And they liked the idea so much they ordered us to do it.”’

Gregg Eckhardt, senior analyst with production and treatment operations at San Antonio Water System, stands in a future wetlands cell below Mitchell Lake. Credit: Scott Ball / San Antonio Report

A successful pilot

While wetlands as a water treatment system are fairly common around the country, no one has ever tried to use wetlands to filter a body of water quite like Mitchell Lake, with its great variation in daily pH levels due to its algae and nutrient-rich state, Eckhardt said.

Hence the small-scale pilot.

In 2019, SAWS planted bulrush, a native freshwater plant resistant to variation in pH levels, on 1.3 acres on the western shore of the lake and made changes to the dam that would allow the utility to better control water levels. SAWS has spent roughly $8 million on the project, so far, said Crowley, including $4 million to buy 283 acres south of the lake.

After 18 months, SAWS declared the pilot a success.

The test wetland allowed SAWS to experiment with how much water the wetlands could effectively treat before becoming oversaturated: between 2 million and 7 million gallons per day, Eckhardt said.

Scaled up, the fully built wetlands will be able to effectively filter hundreds of millions of gallons per day, he added.

San Antonio Water System officials point at preliminary plans for the future wetlands project at Mitchell Lake.
SAWS officials look over preliminary plans for the future wetlands at Mitchell Lake. Credit: Scott Ball / San Antonio Report

The bulrush has also taken off and is actively spreading around the lake, which is exciting for environmental scientists like Eckhardt because it creates more habitat for local species, like roseate spoonbills, white pelicans and yellow-billed cuckoos.

“We learned that it’ll work,” he said. “We were very excited about that.”

A look ahead

Attention at SAWS has now turned to bringing the full-scale wetland to life. A third-party design process is underway, including for a new spillway and a paved hike and bike path on top of the old dam along the lake.

The new spillway is needed so SAWS can control how much water filters through the wetlands, Eckhardt explained. While the existing dam and spillway are still standing, they’re 120 years old. Plans are to route the lake’s water away from the historic spillway to preserve it for visitors to observe.

“When we did phase one, we had to do historical and archaeological surveys and what we learned is that we have four resources down there that are eligible for listing on the National Register of Historic Places,” Eckhardt said. “The spillway is one of them.”

SAWS plans to offer its support to the Texas Historical Commission to mark the spillway on the National Register, Eckhardt said.

The utility is planning roughly six wetland “cells” or areas between the lake and the banks of the Medina River. It is still in talks with some private property owners about acquiring land for the project, Crowley noted, although he added SAWS feels confident about how these discussions are going.

The wetlands project is not the only improvement at Mitchell Lake. As a part of the most recent bond, San Antonio voters approved $6 million for habitat and ecosystem restoration, new connections to existing hike and bike trails and potentially a visitors center. On behalf of SAWS, Crowley recently secured a $3 million appropriation from Congress for an ecosystem restoration study of the lake.

“So yeah, there’s a lot of good things coming this way for Mitchell Lake,” said Eckhardt.

Lindsey Carnett covers the environment, science and utilities for the San Antonio Report. A native San Antonian, she graduated from Texas A&M University in 2016 with a degree in telecommunication media...