Aquatic plants can be a beautiful nuisance

Aquatic plants have played an important role in human history, providing food, medicines and building materials. The ancient Egyptians harvested water lilies for food. They would dry lily seeds and ground them into flour used for bread. Other parts of the lily were consumed raw.

Various species of water lilies are cultivated today in Asia for their fruits, seeds and roots. Water chestnuts (Eleocharis sp.), cultivated in Asia, are actually the fruit of an aquatic plant. Many tribes in Africa use the roots of aquatic plants for food. Wild rice (Zizania sp.), not related to cultivated rice, is collected and consumed in the northern United States and Canada.

Giant reeds (Arundo donax) are frequently used to make thatched roofs, fences, musical instruments, paper, cardboard, cellophane, insulation, fiberboard and even building blocks.

Other commercial uses of aquatic plants include: use as animal food, use as a biofertilizer, a source of methane and ethane, and use as filters in wastewater treatment.

Friend or Foe?

While aquatic plants are a necessary component of a healthy ecosystem, humans do not always consider plants to be beneficial.

Aquatic plants can be a nuisance for boaters that live along the canals and other shallow areas of lakes. They can wrap around boat propellers and are sucked into the engines of personal watercraft. There is rarely a concern for boating in the deeper areas of lakes.

According to the Texas Aquatic Plant Management Society, there are many native aquatic plants that benefit your shoreline. They increase water quality and clarity, stabilize sediment and protect shorelines from erosion. Such plants as the White Water Lily, Tape Grass and Pondweed are not only beautiful, but provide food for waterfowl and are an excellent food source and habitat for fish.

On the other hand, you may find you’ve been visited by an aquatic weed that is not native to Texas. Plants introduced to Texas from other parts of the world can create serious environmental problems because their growth habits and lack of natural controls tend to crowd out native plants and get in the way of recreational use of the water.

Non-native plants that have been introduced to Texas waterways include: hydrilla, water hyacinth, alligatorweed, and water lettuce. These plants are difficult to control and tend to create extensive mats of vegetation that crowd out native plants.

Both native and non-native aquatic plants are frequently classified by their habitat. Some more notable habitats are:

  • Free Floating - plants live unattached to bottom;
  • Emergent - plants live with roots attached to the bottom and with leaves and flowers on top of the water; and
  • Submerged - plants live with roots attached to the bottom and with leaves and flowers below the surface of the water.

The majority of aquatic plants live in the littoral zones of lakes that are less than 10 feet in depth, where adequate light penetrates the water and allows for photosynthesis.

Depending on the depth and shape of individual lakes, the littoral zone may be a narrow strip along the shore or may extend great distances into the lake.

Some free-floating plants can find nutrients in the water but most obtain their food from the sediments in the lake bottom.

Why do aquatic plants overtake areas of the lake?

When the natural system has been disturbed or altered, it is possible for both native and non-native plants to grow to levels that become a nuisance. Natural systems are altered in a number of ways:

  • Poorly functioning septic systems surrounding many lakes in Texas that leak into the water and contribute unnaturally high levels of nutrients into the water.
  • Over application of fertilizers on grass and flowerbeds along shorelines work effectively on aquatic plants as well. As rain or sprinklers allow the fertilizer to run off into the lake, unnaturally high levels of nutrients cause these plants to grow to nuisance levels.
  • Developments where shallow canals are excavated around a lake expand the littoral zone and increase the area where plants can receive adequate light for growth.
  • Construction activities that do not include storm water runoff controls and allow unnaturally high levels of sediment to travel from the land into the water. This sediment inflow over time can contribute to reducing the depth of the lake, thus expanding the littoral zone.

What can I do about these plants?

Because Texas’ rivers and reservoirs are used for both recreation and drinking water, management of aquatic vegetation is regulated under the State Aquatic Vegetation Plan.

According to the Texas Parks and Wildlife Department (TPWD), a treatment proposal must be filed with the TPWD before being undertaken. Control options fall into four basic categories:

  • Mechanical – dragline, cutters, rakes, brooms, mechanical harvesters and bottom barriers;
  • Environmental – lowering water levels, and providing shade;
  • Biological - stocking fish or insects that feast may manage some plants;
  • Chemical (Herbicides) – chemical control will affect fish and insects as well as plants.

To learn about both native and non-native aquatic plants in Texas and treatment options, you may contact the Texas Aquatic Plant Management Society at (972) 436-2215 or the Texas Parks and Wildlife Department at (800) 792-1112.