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South Carolina, like other Southeastern States, is experiencing problems caused by excessive growth of submerged and emergent herbaceous aquatic macrophytes in lakes and streams. The primary problem is interference with boat travel, although water quality problems also occur. Six problem species have been introduced into the State from other continents. The distribution of the most abundant aquatic plants was mapped for 15 lakes and streams in the State in 1985 using a combination of remote sensing techniques and field surveys. In the 15 lakes and streams mapped, the areas most affected by aquatic macrophytes were the Cooper River, Back River Reservoir, Stevens Creek Reservoir, the Savannah River, and Lake Moultrie. The most abundant aquatic macrophytes were Brazilian elodea [Egeria densa), Smartweed [Polygonun dens!florin), Slender naiad [Nalas minor), Pickerelweed (Pontederia cordata), and Water Primrose CLudwigia uruguayensis). INTRODUCTION South Carolina, like other Southeastern States, is experiencing problems caused by excessive growth of submerged and emergent herbaceous aquatic macrophytes in lakes and streams. These aquatic macrophytes, often called aquatic plants or aquatic weeds, are non-woody plants larger than microscopic size that grow in water. Aquatic macrophytes may be free-floating or rooted in bottom sediment. The plants may be entirely submerged or may protrude from the water. The primary problem posed by these plants is interference with boat travel. Many boat launching areas, docks, river channels, and preferred fishing areas become overgrown with aquatic macrophytes in simmer, preventing or greatly hindering access by boat. Another problem associated with excessive growth of aquatic macrophytes is deterioration of water quality. Although the green parts of aquatic macrophytes produce oxygen through photosynthesis during daylight hours, this occurs primarily near or above the water surface. The oxygen-consuning process of respiration takes place throughout the plant, both day and night, and frequently causes depletion of dissolved oxygen in the water coliinn below the photosynthetic zone. Also, senescense and decay of the plants during hot weather in simmer and at the end of the growing season exerts an additional demand for dissolved oxygen. A significant fish kill in upper Lake Marion, South Carolina during August 1986 was apparently caused by movement of anoxic water from beneath aquatic macrophytes to an area where fish were congregated (Jim Bulak, South Carolina Wildlife and Marine Resources Department, oral commun., May 1987). Other problems that have been attributed to excessive growth of aquatic macrophytes are stunting of fish growth and deterioration of aesthetics. Aquatic macrophytes are a natural part of aquatic ecosystems, especially where water is relatively shallow, clear, and warm. Macrophyte growth and sedimentation are the primary processes that are responsible for filling lakes and reservoirs. A moderate level of macrophyte growth is often considered beneficial to a lake or stream, providing cover and food for fish and other aquatic organisms upon which fish feed. Problems arise when the macrophyte growth becomes excessive. Several factors appear to contribute to the excessive growth of aquatic macrophytes in some lakes and streams of South Carolina (Harvey and others, 1987). One factor is the gradual decrease in the rate of sediment transport in recent years in many southeastern streams. Originally quite low during colonial times, the rate of sediment transport increased greatly during the eighteenth and early nineteenth centuries due to erosion related to farming practices in the Piedmont (Patterson and Cooney, 1986). During this period, growth of aquatic macrophytes was probably inhibited by turbidity-induced reductions in light penetration and by unstable substrates. A reduction in acreage of cropland since about 1920, along with improved farming practices and the construction of reservoirs, has begun to reduce the rate of sediment transport. This has resulted in reduced turbidity and greater light penetration in the water column, which has been accompanied by an increase in macrophyte growth, particularly in shallow areas. Another factor in the excessive growth of aquatic macrophytes is the introduction of exotic species of aquatic macrophytes into South Carolina. Many of these species have little competition and few native herbivores feed upon these plants. Some of the exotic aquatic macrophytes introduced into South Carolina lakes and streams are listed in table 1. One of the primary means of introduction of exotic macrophytes is the release of aquarium plants purchased commercially. Once introduced, plants rapidly spread to other water bodies by natural means and by transport of plant fragments on boats, motors, and trailers. Aquatic macrophytes can be controlled to some extent through the use of herbicides, biological control, mechanical harvesting, and water-level fluctuations; however, the control measures are expensive (S.C. Aquatic Plant Management Council, 1984). Surveys of the locations and extent of aquatic macrophyte problems in waters of the State, and of the species distribution within the problem areas are needed if State and local agencies are to make the most effective use of available control measures. Periodic surveys are also needed to determine the effectiveness of control programs and to monitor natural changes in the distribution of aquatic macrophytes. Table 1. Aquatic macrophytes introduced into South Carolina Common name Scientific name Origin Brazilian elodea Egeria densa South America Hydrilla Hydrilla verticillata Eurasia Slender naiad Najas minor Eurasia Parrot-feather Myriophyllum aquaticum South America Alligator-weed Alternanthera philoxeroides South America Water hyacinth Eichhornia spp. South and Central America Purpose and Scope The South Carolina Water Resources Commission, which is the lead agency on the South Carolina Aquatic Plant Management Council, and the U.S. Geological Survey began a cooperative investigation to survey aquatic macrophytes in State waters in 1985. The objectives of the investigation were to determine the areal extent of the significant aquatic macrophyte problems in the public waters of South Carolina, to determine the dominant species in the problem areas, and to document the information on maps that would assist the State and local agencies responsible for the management and control of aquatic macrophytes. The study involved field surveys by boat and remote sensing using aerial photography to map the aquatic macrophytes in 15 lakes and streams in South Carolina. This report presents the results of that investigation. Study areas By agreement among the U.S. Geological Survey, the South Carolina Water Resources Commission, and the South Carolina Aquatic Plant Management Council, 15 lakes and streams were selected for inclusion in this investigation. The lakes and streams selected were relatively large, publically-owned water bodies with significant aquatic plant problems. Certain public water bodies were excluded. State Park lakes were excluded because they were generally too small. Lake Marion, the water body with the best-known aquatic macrophyte problems in the State, was excluded because the distribution of aquatic macrophytes in that lake was being determined as part of the Santee-Cooper River Basin Water-Quality Study by the South Carolina Department of Health and Environmental Control (Welch and others, 1985; Welch and Remillard, 1986). The lakes and streams selected for inclusion in this study are listed in table 2 and their locations are shown in figure 1. Table 2. Lakes and streams included in the study Map reference number Lake or stream name Remark

Distribution of aquatic macrophytes in 15 lakes and streams in South Carolina, 1985