NC State Fisheries and Pond Management Extension-Grass Carp Introduction

Introduction

Plants are important components of the aquatic environment. They form the basis of the food chain, directly or indirectly feeding all of the animals in the system. Plants provide breeding and nesting sites and cover for fishes, waterfowl, and mammals. Plants also supply oxygen through photosynthesis, stabilize the pond or lake bottom, and prevent shoreline erosion. Most aquatic habitats that contain no vegetation are incapable of sustaining an animal population. Consequently, some vegetation is desirable in most streams, lakes, and ponds. Excessive plant growth, however, can cause problems, making a weed management program necessary.

The amount of nutrients in water and sediment and the availability of sunlight for photosynthesis regulate the growth of vegetation in any aquatic habitat. High input of nutrients, particularly phosphorus and nitrogen, combined with large areas of clear, shallow water inevitably lead to excessive growth of algae or other aquatic plants. Once weedy growths become established, they can invade areas of deeper water and may entirely overrun a pond or shallow lake.

Algae and other aquatic weeds:

clog water intakes and distribution systems used for irrigation, public water supplies, and hydroelectric generating plants;
increase sedimentation in flood control reservoirs;
harbor the vectors of human and animal diseases;
interfere with aquaculture;
impede boating access and navigation;
make recreational activities such as swimming, boating, skiing, and sport fishing difficult and dangerous, if not entirely impossible.

Heavy weed infestations, especially of highly invasive, exotic species such as hydrilla (Hydrilla verticillata), Brazilian elodea (Egeria densa), and Eurasian watermilfoil (Myriophyllum spicatum), cause severe habitat reduction, stunt sport fish growth, and reduce the total number of harvestable fish. Several drownings also have been attributed to swimmers becoming entangled in dense growths of aquatic weeds. These examples show the need for vegetation management.

Physical, mechanical, chemical, and biological techniques are available for management of aquatic vegetation. Habitat manipulation such as drawdown, the use of barriers made of plastic or fabric that cover the bottom and prevent plant establishment and growth, and the use of pond dyes to shade out plants are ways to control the environment physically. Mechanical techniques involve the use of either hand labor (for example, raking and seining) or machinery (such as draglines, backhoes, or specialized aquatic harvesters) to remove vegetation from the water. Herbicides can be applied either over the surface or into the water column to kill unwanted vegetation. With biological control, natural enemies such as insects or fish are released into aquatic areas to feed on the weedy vegetation and maintain its density at an environmentally or economically acceptable level. Each of these techniques has its advantages and disadvantages. Several of the techniques are frequently integrated into a weed management program.

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