Aquatic plants hold a fascination for gardeners, whether they have a large pond or a bird bath. Aquatic plants can be divided into (1) algae or (2) rooted water plants. Algae are simple plants that lack true roots, leaves, or flowers. They may occur as single cells, colonies, filaments, or advanced forms (muskgrasses or stoneworts), growing to a height of 2 to 3 feet and resembling rooted plants.

Algae may occur as free-floating surface scums; dense, surface- or bottom-tangled mats; attached on rooted plants or submerged objects; or motile, individual forms dispersed throughout the water. Since these are primitive, nonflowering plants, few homeowners would intentionally introduce them into garden ponds. However, certain algal types require no conscious introduction, as birds frequently do that job. Standing water outdoors will always contain algae, and small garden ponds with high nutrient inputs may become overgrown with algae.

Control algae by introducing algae-eating fish and shading the surface of the water with plants.

Rooted water plants have true stems, roots, leaves, and flowers. They may be EMERGENTS, such as cattails, with most of their leaves, stems, and flowering parts exposed to air; FLOATING LEAF PLANTS with only the leaves on the surface; or SUBMERGED with the leaves, stems, and reproductive structures occurring underwater.

Emergent plants, sometimes called marsh plants, grow above the water surface in shallow, shoreline areas of lakes, ponds, and slow-moving rivers. Although major portions of the plants are fully exposed to air, they are rooted in bottom sediments. Common emergents found in some waters include cattail, arrowhead, pickerelweed, bulrush, rushes, bur reed, and smartweed.

Certain of these, such as cattail and arrowhead or duck potato, produce edible plant materials that were an important food source to native Americans and are still consumed today. Cattail flower spikes and leaves are dried and used in decorations. Rushes and reeds are woven into baskets and mats. Many of these are an important source of cover and food for fish and wildlife.

When incorporating emergents into your garden pond, you need to make sure plant heights and growth forms are appropriate for the size of your pond. In most cases, you will have to manually remove some plants during each growing season to insure that one or two species do not overpopulate your pond.

Floating leaf plants may be rooted in the bottom muds or be unattached and float freely on the surface, such as duckweed and water meal. Plants with the smallest and largest leaves are in this group. Wolffia or water meal has a single, oval-shaped leaf that is less than 1/16 of an inch in diameter.

The lotus (Nelumbo lutea) has round leaves that exceed 24 inches in diameter. The tiny, floating plants can reproduce rapidly under favorable conditions and blanket a pond with a green scum. Lotus and waterlilies (floating leaf plants) produce some of the showiest flowers of the plant world. The white water lily (Nymphaea odorata) with fragrant, white or pink flowers is a favorite ornamental in garden ponds.

Submerged plants (water milfoil, elodea, watercress, wild celery, and pond weed) grow with most of their parts below the water surface although flowers and seed stalks may, at certain times of the year, extend above the surface to insure pollination by wind and insects. Since these plants depend on the water for support, they are limp and unable to support themselves in an upright position when removed from water.

Submergent water plants are important sources of food and cover to fish and wildlife. Wild celery, Vallisneria americana, is a valuable food source for waterfowl and is often planted on wildlife refuges. Frogbit or American elodea (Elodea canadensis) and Brazilian elodea (Egeria densa) are commonly sold as aquarium plants.

Certain submergents, such as watermilfoil and hydrilla, can form dense, impenetrable, weed beds throughout lakes and ponds, reducing water movement, causing siltation, depleting dissolved oxygen, and changing the whole character of an aquatic ecosystem. If submergents become established in your garden pond and you are not able to adequately remove them through manual techniques, you may have to drain the pond and allow these plants to dry to a powder. These plants spread by fragmentation, and one small fragment can reintroduce the plant into your pond.