Plants that grow in fresh water include those that float, flower and/or produce interesting leaves. If you're thinking about planting a water garden, think about the pond environment, for instance, water depth and sunlight. Also, some water plants can be aggressive and take over a pond. Check your state's list of such plants before ordering water plants from catalogs.
Floating Leaf Plants
The leaves of floating plants cut sunlight, creating shade and controlling algae growth. According to Texas A&M's Water Gardens in Texas online guide, 50 to 75 percent of a pond should be covered in floating plant cover. Water lilies serve the purpose of filtering sunlight in a pond and most varieties themselves need much sunlight. Tropical water lilies (Tina, Panama Pacific, Director Moore and others) include varieties that bloom at night. Hardy lilies (Comanche, Attraction, Virginia and others) bloom all day, and some varieties flower in different shades as the plant ages. Though lotus plants are also floating, they won't cover a pond surface the way lilies will.
Plants living beneath the surface of a pond oxygenate it, allowing animals like fish to live in the water. Submerged plants have roots, but the plants only use them to stay anchored. Thus, for a water garden you can pot submerged plants in soil, sand or gravel. Some kinds of submerged plants try to take over ponds, especially earthen ponds. Choose carefully. water milfoil, with a lot of foliage, Vallisneria, a large grassy plant, and dwarf Sagittaria, a small, grassy specimen, are all submerged plants.
Floating Plants that Move
Plants that float across the surface of water as the wind blows cast shadows for fish and make water gardens interesting. Moving plants include water lettuce, fairy moss, water poppy, which produces yellow flowers, and water hyacinth. Instead of being planted in pots, tubs or baskets like the other kinds of plants in a water garden, these can be put directly on the pond.
Marginal plants are those that can grow in the margins of a pond--that is, they can grow in boggy soil. The area might be more water than soil, constantly wet soil or moist soil. Marsh plants include cattails; the aggressive Iris pseudacorus, the blue, red and Bryce Leigh irises; Rosea Plena lotus, with large, fragrant, pink flowers; and Mrs. Perry D. Slocum lotus, with fragrant blooms ranging from cream to yellow to pink.