Within a lake or pond, aquatic plants grow in an area known as the littoral zone--the shallow transition zone between dry land and the open water area of the lake. In Minnesota waters, the littoral zone extends from the shore to a depth of about 15 feet, depending on water clarity. The shallow water, abundant light, and nutrient-rich sediment provide ideal conditions for plant growth. Aquatic plants, in turn, provide food and habitat for many animals such as fish, frogs, birds, muskrats, turtles, insects, and snails. Protecting the littoral zone is important for the health of many of a lake's fish and other animal populations.
Aquatic plants are grouped into four major categories:
As Figure 1 illustrates, each of the four types of aquatic plants favors a certain water depth. Typically, however, the growth areas are not sharply divided. Expect to see overlap in growth--submerged plants, for example, are often interspersed among floating-leaf varieties.
The width of the littoral zone will vary within a lake and among lakes. In places where the slope of the lake bottom is steep, the littoral area may be narrow, extending several feet from the shoreline. In contrast, if the lake is shallow and the bottom slopes gradually, the littoral area may extend hundreds of feet into the lake or may even cover it entirely.
Cloudy or stained water, which limits light penetration, may restrict plant growth. In lakes where water clarity is low all summer, aquatic plants will not grow throughout the littoral zone but will be restricted to shallow areas near shore.
Other physical factors also influence the distribution of plants within a lake or pond. For example, aquatic plants generally thrive in shallow, calm water protected from heavy wind, wave, or ice action. However, if the littoral area is exposed to the frequent pounding of waves, plants may be scarce. In a windy location, the bottom may be sand, gravel, or large boulders--none of which provides a good place for plants to take root. In areas where a stream or river enters a lake, plant growth can be variable. Nutrients carried by the stream may enrich the sediments and promote plant growth, or suspended sediments may cloud the water and inhibit growth.
In summary: Where aquatic plants grow and how abundant they are may vary greatly from lake to lake, and even within a lake itself. Qualified lake specialists can help you decide what you should or should not do. DNR regional Fisheries staff can help direct you to available resources and aquatic plant specialists.