Aquatic plants become weeds when they impair or prevent use of the pond or waterway.
Mark Hartle, biologist for the Pennsylvania Fish and Boat Commission, says aquatic plants vary according to the environment they are placed in, and control measures are dictated by what type of plant life is choking off the pond. Surrounding land use also can influence aquatic plant growth, either by acting as an effective filter for excess water and nutrients, which limits growth, or by failing to filter nutrients, which can cause excessive aquatic plant growth. The most widely distributed of all aquatic plants, algae can be subdivided into three types. They have a skunky odor when crushed. Most plants in this category grow in deeper water and are rooted on the bottom.