For officials testing Lake Waco’s water for evidence of invading zebra mussels, a negative is a positive.
And the most recent test by Texas Parks and Wildlife Department turned up negative, showing no traces of zebra larvae or DNA material in samples collected July 10 at several points around the lake.
“That does not mean zebra mussels are not there or that they haven’t established themselves in the lake, but it’s certainly an encouraging sign,” said Brian Van Zee, TPWD inland fisheries regional director based in Waco.
The discovery last summer of a small zebra mussel colony near the Ridgewood Country Club boat ramp raised worries that the mollusks could quickly dominate the lake, clogging intake pipes and upsetting the ecosystem.
Officials with the city, state and U.S. Army Corps of Engineers reacted to the threat last fall by smothering the colony with a football-field-size tarp.
This March, city employees discovered a few zebra mussels around the boat ramp, but said they were “sickly” and might not be successful at reproducing.
Van Zee said mussel populations have to be dense enough that their sperm and eggs can find each other in the water, and the tarp project made spawning more difficult.
“If they’re not close enough, the few that are left in the water could die out of old age,” he said.
Van Zee said spawning season for zebra mussels starts in the fall, when water temperatures are between the mid-50s and high 70s.
He said monitoring planned for the fall should give a clearer picture of whether zebra mussels have become established.
“We’re optimistic, but we want to be cautious in saying that we haven’t been infested,” he said. “I think it’s going to take a few months.”
Lake Waco Manager Heath McLane said the effort to smother the mussels was worthwhile and provides hope, even though some officials at the time the tarp was laid thought the move was a Hail Mary.
“The city tarping them was huge,” he said. “It definitely held them back spawning for a year and gave us a chance. Maybe, just maybe, we’re going to dodge a bullet.”