Aquatic macrophytes are aquatic plants that are large enough to be apparent to the naked eye; in other words, they are larger than most algae. The general term "aquatic plants" usually refers to aquatic macrophytes, but some scientists use it to mean both aquatic macrophytes and algae. (Note: Large algae such as Nitella and Chara are also included in the category of aquatic macrophytes.)

Aquatic macrophytes characteristically grow in water or in wet areas and are quite a diverse group. For example, some are rooted in the sediments while others float on the water's surface and are not rooted to the bottom. Aquatic macrophytes may be native to an area or they may have been imported (referred to as non-native or exotic).

Most aquatic macrophytes are vascular plants, meaning they contain a system of fluid-conducting tubes, much like human blood vessels.

In the eye of the beholder... An aquatic weed problem is often defined differently by people who use a waterbody in different ways.

Even though they are quite diverse, aquatic macrophytes have been grouped into three general categories:

• submersed aquatic plants primarily grow completely below the water's surface (go here for more info about submersed plants);

• emersed aquatic plants are rooted in the sediments and protrude up above the water's surface (go here for more info about emersed plants);

• floating and floating-leaved aquatic plants can be rooted to the bottom, or be completely free-floating, and also have leaves that float on the water's surface (go here for more info about floating and floating-leaved plants).