By Waterline Weed Co. · Updated
Hydrilla at a glance
| Scientific name | Hydrilla verticillata |
| Type | Rooted, submerged perennial aquatic plant |
| Origin | Native to Asia; introduced to the U.S. through the aquarium trade in the mid-1900s |
| Status in Texas | Prohibited exotic species (Texas Parks and Wildlife); also a federal noxious weed |
| Where it grows | Lakes, reservoirs, ponds, and slow rivers, from shallow edges into deeper, clear water |
| How it spreads | Stem fragments, buds (turions), and underground tubers |
How to identify hydrilla
- Leaves in whorls: small, pointed leaves grow in rings around the stem, usually 4 to 8 per ring (often 5).
- Toothed edges: leaf edges have tiny saw-like teeth, and the underside of the midrib often has small spines. Run a strand through your fingers and it feels rough.
- Long, branching stems: stems grow up from the bottom and branch heavily near the surface, forming a thick canopy or mat.
- Tubers in the mud: pull a plant up with the roots and you may find small, potato-like tubers attached below the sediment line.
Hydrilla vs. look-alikes
Hydrilla is often confused with Elodea (American waterweed) and Egeria (Brazilian waterweed). Elodea usually has leaves in whorls of three and feels smooth. Egeria has larger, bushier leaves, usually in whorls of four or more, that also feel smooth. The quick field test is texture: if it feels rough and scratchy, think hydrilla. For a definite ID, send a clear close-up photo to a local extension office or to us.
Why hydrilla is a problem
- Boating: it wraps props, clogs cooling-water and jet-pump intakes, and blocks slips and boat lanes.
- Swimming: dense strands hide the bottom and wrap around arms and legs.
- Docks and lifts: mats build up around pilings, cables, and cradles.
- Water quality: when large mats die back and decay, they can lower oxygen in the water.
- Crowding out native plants: it grows up to the surface and shades out other vegetation.
How it spreads
Hydrilla is very good at making more of itself. Broken stem fragments can drift away and root. Compact buds called turions break off and sink. Tubers in the sediment can survive for years before sprouting. That's why boats and trailers moving between lakes are a major way it spreads, and why Texas asks boaters to clean, drain, and dry everything before leaving a lake. More on why it comes back.
What to do if you have hydrilla at your dock
- Don't mow or chop it and leave the pieces. Fragments can start new plants.
- Remove it at the base and collect everything, either yourself or with a crew.
- Dispose of it away from water and never move it to another lake or pond.
- Plan for regrowth with follow-up clearing during the growing season.
Frequently asked questions
Is hydrilla illegal in Texas?
Hydrilla is on the Texas Parks and Wildlife Department's list of prohibited exotic aquatic plants, so it generally can't be possessed, sold, or transported. Removing it from your waterfront is a different thing from moving or selling it. Just don't relocate it to other water.
Is hydrilla harmful to people or pets?
Hydrilla itself isn't known to be toxic. The practical risks are entanglement for swimmers, hidden bottoms, and damage to boat engines. Dense mats can also host algae in some conditions, so use common sense about swimming in stagnant, matted water.
How fast does hydrilla grow?
In warm, clear water during the growing season, hydrilla can grow very quickly, and it's often reported to add around an inch of stem a day in good conditions. That's why an area can go from clear to matted within a single summer.