Hydrilla (D-Hyrdilla, M-Hydrilla)

Invasive D-hydrilla (Hydrilla verticillata) typically grows upward first, forming dense canopy mats during summer. But an open understory often exist in which those big bass can hide. Fish heavy punch baits. If you can get them below the top layer, you should get a bite.

Two biotypes of invasive hydrilla exist in TVA reservoirs: monoecious (M-hydrilla) and dioecious (D-hydrilla). While the two may look similar, the growth habits of each are very different. D-hydrilla often appears larger and more robust than M-hydrilla.

Seasonal Techniques

Spring—D-hydrilla will be some of the only plant material to make it through the winter so finding these mats can provide for some early grass fishing. M-hydrilla, on the other hand, will be sprouting from tubers creating an emerging grass edge early in the spring.

Summer—D-hydrilla typically grows upward first, forming dense canopy mats during summer. But an open understory often exist in which those big bass can hide. Fish heavy punch baits. If you can get them below the top layer, you should get a bite. M-hydrilla is much more difficult to fish in summer. It first covers most of the bottom, then begins growing toward the water's surface. This growth habit often leads to a “wall-like” bed of vegetation with few holes and very little understory for fish to hide in. Flip holes created by underwater obstructions (logs, rocks) or fish the edge of these impenetrable mats.

Fall—Both D-hydrilla and M-hydrilla provide excellent cover for the ever popular frog bite of fall. M-hydrilla will begin to die back in middle to late fall, leaving open areas beneath floating mats. D-hydrilla will continue to maintain the canopy and understory which are conducive for big bass. As these and other plants decay, a “slime” of algae will begin to form, and fish will take advantage of newly released nutrients. Find the combination of decaying plants and “slime,” and give them all you’ve got.

Winter—D-hydrilla will slow growth and die back some, but should maintain clumps of vegetation around existing root crowns. This will be some of the only grass available for fishing in winter, so target isolated clumps with a slow presentation. M-hydrilla will die back completely in winter, so little structure is left behind to target.

Habitat Value

Fish—D-hydrilla provides good habitat and safety structure for fry and juvenile sport fish as well as a refuge for baitfish. An open understory can also provide foraging opportunity for predatory fish. M-hydrilla can inhibit fishing access during the peak of summer, but does provide edge habitat.

Waterfowl—Both species can be a key resource for waterfowl in the Tennessee Valley, not because of their nutritional value, but because of their abundance as invasive species. Hydrilla has been associated with avian vacuolar myelinopathy (AVM) in other areas, which can negatively impact water birds and predatory birds like eagles.  

Identifying Features

What It Looks Like—Small, pointed leaves whorled around the stem, most often in sets of four to six. Distinguishing the two biotypes from one another can be very difficult, but an apparent size difference (D-hydrilla being larger) can often be seen.

Where to Find It—In TVA reservoirs, hydrilla is one of the most abundant plants in the system. Being a very aggressive plant and growing out into deep water can make this plant one of the easiest to find.  

Similar Species—This species resembles Canadian elodea and Brazilian elodea. Canadian elodea is often much smaller and whorls are in sets of three or less. Brazilian elodea is often larger and does not produce the characteristic tubers of hydrilla.  

Drawbacks

Hydrilla is by far the most costly plant to manage in the TVA system. Reportedly growing one to four inches per stem per day, this plant can quickly impede all recreational activities, including fishing access. Cost to manage: $$$$$ out of $$$$$.