“Infested” is not a word you want to hear in reference to anything. But that’s exactly the word the Texas Parks and Wildlife Department is using to describe Lake Austin.
The lake is infested with zebra mussels, which means there's a reproducing population in the water. The invasive shellfish are also now present in Lady Bird Lake, and what comes next could be a total upheaval of the local ecosystem.
So what does all this mean?
What are they?
At first glance, the small, striped triangular mussels don’t look very threatening. They’re about the size of a nickel, with brown and yellow stripes. But, in large enough numbers, they wreak havoc. In some lakes, the biomass of zebra mussels becomes greater than that of every other creature in the lake combined.
Originally from the Caspian Sea, they hitched a ride to North America in the ballast water of ships back in the '80s and have been spreading through the continent ever since.
The populations are so dense in some places that you can sometimes find “thousands-per-square-meter” says Robert McMahon, a mussel researcher at UT Arlington.
“They’re literally filtering the water over in a lake,” he says. “Depending on how dense it is, they might turn over all the water in a lake every week.”
That robs other small creatures of food. The creatures that eat those creatures then go hungry, and so on.
In Austin, that could mean a “top-to-bottom change in the whole ecosystem” says Liz Johnston, an environmental program coordinator with the City of Austin.
Going clear
One of the more visible effects may be increased water clarity.
“That’s what they’ve seen in northern lakes,” Johnston says. “It may look beautiful to people because it’ll be crystal clear and you'll think, ‘This is beautiful clean water,’ when really it’s not the way it’s supposed to be."
That clarity allows sunlight to reach deeper into the lake. That could encourage more plant growth, including invasive hydrilla and algae blooms that sometimes make our drinking water taste funny.
“If there’s a really bad bloom and the water’s clearer, it may actually make the lake blue-ish green at times,” Johnston says.
A threat to water treatment – and to bare feet
The arrival of zebra mussels could also mean no more walking barefoot in or near waterways.
“They live quickly and die quickly,” Johnston says. “All of the shells will get deposited on the banks. They’re very sharp to walk on … It will make any beaches along our reservoirs not pleasant to walk on barefoot.”
The mussels also clog water-intake pipes. In other places, utilities have spent millions of dollars dealing with them.
In Austin, the city water utility is calling the mussels a “serious threat to Austin’s water treatment plants.”
A report from Austin Water from last year said the utility will consider applying special coating to water infrastructure and chemical treatments to battle the mussels.
Lakes become contagious
“If you have a boat in the water, they like to attach to hard surfaces,” Johnston says.
“On Lady Bird Lake, we don't have a lot of motor boats, but we do have people coming in and out on their standup paddle boards and kayaks that could potentially be transferred into other systems.”
That means, from now on, anyone who brings a boat to Austin’s lakes should wash it and let it dry, or risk spreading the mussels.
Barton Springs at risk
Now that zebra mussels are in Lakes Austin and Lady Bird, don’t think they’ll stay put. Decker Lake is fed by the same water, so it’s a safe bet the mussels are already there, too.
Johnston says Barton Springs is also at risk.
Upstream, she says, catfish could disperse zebra mussel larvae into spring that feeds the pool. Downstream, swimmers at “Barking Springs” in Lady Bird Lake could also transfer them to Barton Springs Pool, if they decide to jump into the pool after a downstream swim.
Nothing can be done
Here’s the kicker: The City of Austin says there’s no way to safely get rid of zebra mussels.
Some companies tout solutions to the pests, and there are some zebra mussel control experiments underway. But, Johnston says, there is still no proven way to wipe out the mussels without causing damage to the surrounding ecosystem. That means we are stuck with them for the foreseeable future.
Looking for some good news?
Not every lake makes an ideal home for zebra mussels, so it’s possible they won’t proliferate in Austin to the point where they cause maximum harm.
Experts say the coming years will show us exactly how severe their impact could be.
