Zebra mussels are not supposed to be an East Texas problem.
The water quality in reservoirs east of Texas Highway 19 is supposed to be too soft for the invasive mussels to flourish.
Signs that the mussels are spreading across the state continues if not in their actual discovery than at least the discovery of their DNA in ongoing water monitoring, a sign that they are or have been there.
However, zebra mussel DNA was recently discovered in three more Texas lakes, including two in East Texas – Lake Fork and Lake Tawakoni causing a bit of alarm.
The third lake, Lake Grapevine, comes as no surprise because of its proximity to other lakes in the Trinity River basin where the mussels have been found. At this point, however, no mussels have been discovered on Grapevine, but the last three water samples from the lake have tested positive for their existence.
Although situated on the Sabine River, the discovery of zebra mussel DNA isn't a major surprise on Tawakoni. Located west of Highway 19, it is already among the lakes where fishermen are required to drain all water from their boats before leaving the boat ramp.
Lake Fork is a different story.
"Fork and Tawakoni are on the cusp for water quality parameters for developing zebra mussels," said Craig Bonds, TPWD Fisheries regional biologist.
Bonds explained that the mussels, introduced into the Great Lakes in the 1980s through the discharge of ballast water from European ships, can only thrive in hard water.
"According to the experts out there, they have to a specific alkalinity level below which they suspect zebra mussels won't develop dense populations because they need so much alkalinity to build their shells," he explained.
However, Bonds added that doesn't mean a lake with soft water may not develop a population, it just probably won't grow to the density it might at lakes in the central and southern portion of the state.
The biologist said the results from Tawakoni and Fork were weak positives.
"That tells us at some point the lake had exposure to dead zebra mussels or a small number of live mussels that didn't develop into a population," Bonds said.
He added this is not the first time testing has shown positive markers for zebra mussel DNA on an East Texas lake without colonies developing.
"Caddo lake had a very weak positive, but it never developed a population. We don't know if it was the soft water or if it only had one or more exposures to dead shells or it didn't produce a reproducing population," Bonds explained.
Other East Texas lakes that are highly vulnerable to producing viable populations include Cooper, Cedar Creek and Richland Chambers. Boaters are also already required to drain their boats at Cedar Creek and Richland Chambers.
Although Lake Fork and others are not considered high risk reservoirs at this time, Bonds said boaters should still drain livewells and lower units at the ramp on it and any other lake at the end of the day.
He also suggests keeping an eye out for mussels attached to boats, motors, piers and bridge pilings. While there are native species of mussels found in East Texas, none are able to attach to something like a zebra mussel. If they are discover TPWD or the local water authority should be contacted.