Zebra Mussels in Texas: Spread, Clean-Drain-Dry Law, and Penalties

Zebra mussels in Texas have spread to 34 lakes and seven river basins, and state law now requires every boater to clean, drain, and dry their vessel before leaving or approaching any public fresh water. A first violation is a Class C misdemeanor with fines up to $500. Repeat offenses can bring $2,000 fines and up to 180 days in county jail.

Where Zebra Mussels Have Spread

The Texas Parks and Wildlife Department sorts affected water bodies into three tiers. An “infested” lake has a confirmed, reproducing population. A “positive” lake has had multiple detections of larvae or adults but no confirmed breeding population. A “suspect” lake has had just one verified detection.¹

As of the most recent TPWD data, 34 Texas lakes carry the infested classification, spanning most of the state’s major reservoir systems:²

North Texas: Texoma, Ray Roberts, Lewisville, Grapevine, Eagle Mountain, Worth, Bridgeport, Richland Chambers, Livingston, and Dean Gilbert
Central Texas: Travis, Austin, Lady Bird, Buchanan, Inks, Lyndon B. Johnson, Marble Falls, Canyon, Belton, Stillhouse Hollow, Georgetown, Granger, Pflugerville, Walter E. Long, and Placid
West and South Texas: Amistad, Brownwood, Hords Creek, Medina, Diversion, Nasworthy, O.H. Ivie, Randell, and Town Center Pond

Zebra mussels or their larvae have also been found in seven river basins: the Red, Trinity, Brazos, Colorado, Guadalupe, San Antonio, and Rio Grande. Lakes Dunlap, Fort Phantom Hill, Lavon, and McQueeney are classified as positive. Lake Ray Hubbard near Dallas currently holds “suspect” status after a single detection.²

These classifications change as monitoring continues. TPWD maintains an updated map and lake-by-lake list on its website, and checking it before you launch is the simplest way to know what you’re dealing with.

Why They Cause So Much Damage

A single female zebra mussel can release up to one million eggs in a spawning season, and the young reach reproductive maturity within a year.³ That reproductive rate is the engine behind every other problem the species causes.

As filter feeders, zebra mussels consume enormous quantities of phytoplankton, the microscopic algae at the base of the aquatic food chain. Dense populations filter so much water that they redirect energy away from open-water food webs and toward the lake bottom, cutting the food supply for zooplankton, larval fish, and other species that depend on plankton. Infested water bodies show lower chlorophyll concentrations, reduced zooplankton populations, and declining growth rates among open-water fish.⁴

Native freshwater mussels take the worst of it. Zebra mussels colonize their shells by the thousands, physically weighing them down and restricting their ability to move, feed, and reproduce. Heavy infestations kill off more than 90 percent of native mussels in affected areas within four to five years.⁵

The same attachment behavior wrecks infrastructure. Zebra mussels colonize the insides of raw water intake pipes, generator cooling systems, and other submerged equipment, gradually restricting water flow. Hydroelectric facilities have to shut down powerhouses to scrape mussels out of piping, routing water through spillways and losing output in the meantime.⁶ Municipal water treatment plants face the same problem on their intake screens and internal piping. Nationally, zebra mussel damage to water infrastructure and industry runs about one billion dollars a year.⁷

What the Law Requires: Clean, Drain, Dry

Texas law requires you to drain all water from your boat and gear before leaving or approaching any public fresh water body. This is an enforceable regulation under 31 Texas Administrative Code Section 57.1001, and it applies to every type and size of watercraft, from bass boats to kayaks.⁸

Clean

Before you leave the boat ramp area, remove all visible plant material, mud, and debris from the hull, trailer, and attached equipment. Texas law makes it illegal to transport any harmful or potentially harmful aquatic plant clinging to your vessel, trailer, or towing vehicle. Anything you scrape off goes on land at the ramp, never back in the water.⁹

Drain

Empty every compartment that holds or could hold water: bilges, livewells, bait buckets, ballast tanks, and the engine’s cooling system. Zebra mussel larvae, called veligers, are microscopic, so water that looks perfectly clean can still carry thousands of them. Pull the drain plug and leave it out during transport. The regulation requires draining before you use any public roadway other than the boat ramp itself.⁸

Draining also covers bait buckets and live wells. You cannot legally haul lake water home with your leftover bait. To keep live bait between trips, transfer it to fresh, uncontaminated water before you leave the ramp.⁹

Dry

After cleaning and draining, let the boat and all equipment dry completely before launching in another water body. Adult zebra mussels can survive out of water for several days in cool, humid conditions, so drying is what finishes the job. The longer the boat sits in direct sun between trips, the better. The Texas regulation doesn’t set a fixed drying period, but a week in summer conditions is a reasonable precaution after a trip to infested water.

Penalties for Violations

Failing to drain your vessel or transporting aquatic invasive plants is a criminal offense under the Texas Parks and Wildlife Code. A first violation is a Class C misdemeanor with a fine ranging from $25 to $500.¹⁰

Repeat offenses escalate to a Class B misdemeanor, with fines up to $2,000, up to 180 days in county jail, or both.⁹

Possessing or transporting live zebra mussels is separately illegal under Texas Parks and Wildlife Code Section 66.007, which prohibits the import, possession, sale, or placement of exotic harmful shellfish into Texas public waters except under a department permit. Intent isn’t required. Knowingly leaving mussels attached to your boat and hauling it down the highway counts as possession.¹¹

Texas Game Wardens enforce these rules at boat ramps and on public roadways. They check that drain plugs have been pulled, look for attached organisms, and verify that no water remains in compartments. Texas relies on warden patrols and public education rather than fixed roadside inspection stations.

Extra Decontamination for Slip-Kept Boats

Clean, drain, and dry is the legal minimum. If your boat has been sitting in an infested lake, particularly in a slip, you may need to go further. Hot water is the most effective field treatment. Water at 140°F at the point of contact kills both adult mussels and larvae. When pressure-washing, move the wand slowly enough that each area gets at least 10 seconds of sustained contact, and give hard-to-reach spots a full 60 seconds.

Run the motor for one to two minutes using a hot water source connected through a muff fitting to flush the cooling system. Internal ballast tanks and water storage systems should be flushed with water at 120°F to 130°F for at least two minutes.

If you find attached mussels on equipment you’ve already removed from the water, you can kill them with a bleach soak: one-third cup of regular, unscented household bleach per gallon of water, with items submerged for at least 10 minutes. The step people skip is disposal. That bleach water must go down a household drain, never a storm drain, ditch, or waterway, where it could reach and damage the local ecosystem.¹²

How to Identify a Zebra Mussel

Zebra mussels are small, roughly thumbnail-sized, though they can reach about an inch and a half. Their shells have a distinctive D-shape with a flattened underside, so when you set one on a table it stands upright rather than rolling to one side. Color varies widely from light tan to dark brown, often with the alternating dark and light stripes that give the species its name. Not every specimen has obvious stripes, so shape matters more than color.¹³

The clearest giveaway is attachment. Tiny byssal threads on the hinge side of the shell let zebra mussels glue themselves to boat hulls, dock pilings, intake pipes, and other submerged equipment. Native Texas mussels live partially buried in sediment and don’t attach to structures. A small mussel cemented to your boat or trailer is almost certainly a zebra mussel.¹³

One native species, the dark false mussel, has a similar triangular shell and can cause confusion. The key difference is a small tooth-like projection near the pointed end of the dark false mussel’s shell that zebra mussels lack. Zebra mussels also have an obvious lengthwise ridge running down each side of the shell and a shelf-like internal structure called a septum at the pointed end. If you crack open a suspect shell and see that internal shelf, it’s an invasive mussel.¹³ Getting this right matters, because Texas has more than a dozen native freshwater mussel species federally listed as endangered or threatened, and destroying one of those does the same kind of damage zebra mussels already do.¹⁴

How to Report a Sighting

If you find zebra mussels at a lake or river where they haven’t been documented before, report it. Early detection gives resource managers a chance at slowing the spread. TPWD asks the public to submit reports through the TexasInvasives.org reporting portal, which forwards the information to the appropriate authorities. Include the location, a description of what you observed, and ideally a photo. Collecting a sample helps confirm identification, but don’t transport live mussels. Freeze or dry the specimen first, or photograph it in place.²

1
Texas Parks and Wildlife Department. TPWD to Standardize Zebra Mussel Classification System
2
Texas Parks and Wildlife Department. The Zebra Mussel Threat
3
U.S. Geological Survey. Zebra Mussel (Dreissena polymorpha) – Species Profile
4
U.S. Geological Survey. Impacts of Dreissena polymorpha – Ecological
5
U.S. Geological Survey. Impacts of Dreissena polymorpha – Native Mussels
6
U.S. Army Corps of Engineers. U.S. Army Corps of Engineers Moves to Eradicate Invasive Species
7
U.S. Geological Survey. A Cost-Benefit Analysis of Preventative Management for Zebra and Quagga Mussels
8
Legal Information Institute. 31 Tex. Admin. Code 57.1001 – Draining of Water from Vessels Leaving or Approaching Public Fresh Water
9
Texas Parks & Wildlife Department. Clean, Drain, Dry Your Boat
10
Texas Parks & Wildlife Department. Possession and Transport of Exotic Aquatic Species
11
State of Texas. Texas Parks and Wildlife Code Section 66.007 – Exotic Harmful or Potentially Harmful Fish and Shellfish
12
U.S. Fish & Wildlife Service. Zebra Mussel Disposal
13
Texas Parks & Wildlife Department. Identifying Invasive Zebra and Quagga Mussels
14
U.S. Fish & Wildlife Service. Texas Freshwater Mussels