Carp help destroy underwater plants in Lake Austin

FILE - Lake Austin (KXAN File Photo)
FILE - Lake Austin (KXAN File Photo)

AUSTIN (KXAN) — A harsh winter, birds, and thousands of carp are all reasons Texas Parks and Wildlife believes its last study on Lake Austin found no underwater vegetation.

The lake is a place for recreation, fishing, and escape. It also helps mitigate flooding and its one of the lakes where the city draws water to treat for drinking water. The vegetation on the lake helps prevent erosion, keep water clear, and provides habitat for animals.

“My oldest son, he’s three,” said John Ward, an angler with Texas Tournament Zone. “I’ve taken him out here fishing with his grandfather before and back then the lake was a little bit different, a little clearer.”

Ward believes the city put too many sterile grass carp into the lake, with the approval of the state.

“You can still see some reeds right on the edge of the lake there,” he said. “They used to come out a good 20 yards and they were solid all the way down.”

Catching a big bass is harder now than it used to be, Ward added.

The number of carp the city put in the lake exploded in recent years. The city was combating record growth of the invasive hydrilla plant. They believe it poses safety risks and can lead to flooding. As the hydrilla grew, and didn’t go away, the city kept stocking sterile grass carp to eat it. According to stocking records, 6,000 carp entered Lake Austin in December 2011. In 2012 the city put in more than 17,000 more carp. Then, 9,000 more of the fish went into the lake in May 2013. In those 18 months officials stocked the lake with more carp than in the entire previous seven years combined.

“What I believe is that we stocked as many carp we needed to stock to see a reduction in hydrilla,” said Marcos De Jesús with the Texas Parks & Wildlife Department. “Unfortunately, because of the circumstances that are beyond our control, it turned out to be too many.”

De Jesús also does vegetation studies on the lake. The lake went from having record amounts of hydrilla to no observed underwater vegetation.

“I wasn’t happy (when I saw that) because obviously our part of the equation is to maintain aquatic vegetation,” said De Jesús. “As a biologist my efforts now are concentrated to actually restore that vegetation.”

it wasn’t just the carp, De Jesús said. A harsh winter and other animals that eat plants are also to blame.

“You know, so it’s a learning experience,” said engineer Chris Herrington with the City of Austin Watershed Protection Department. “And so we went off scientific literature and worked with our partners including Texas Parks and Wildlife.”

The city maintains Austin was acting on the best information it had, working with partners.

“[Hydrilla] grows very quickly and it can out compete our native plants and it can actually damage the lake for its primary purposes which is flood control, water supply, and then hydropower generation,” said Herrington.

But is the lack of vegetation damaging Lake Austin?

“It is,” said Herrington. “We want a healthy and diverse vegetation community that’s primarily populated with our native and adaptive species.”

“But I think things we could do is actually improve habitat by adding habitat to the lake, sunken brush piles for example,” De Jesús added. “That’s great for fishing. And that’s something we’re planning to do. We’re also planning to remove some of the grass carp.”

“How long is that going to take?” Ward wanted to know. “That’s a question everyone wants an answer to.”

It’s a question without a clear answer. Texas Parks and Wildlife plans to finalize its actions in the next couple months.

The city is also trying to get native species to grow. Although the state maps show no vegetation, the reports point out there are caged plants on the lake. The city started plantings in 2004.

“It’s very difficult to balance all the interests,” said De Jesús, “and our job is to make sure we get together as a focus group to make sure all these interests are met. Our interest is to make sure that we have habitat for fish and wildlife and that’s what we’ve tried to do over the years.”

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