Lakes and Aquatic Plants

Lake aging is a slow, natural process whereby lakes collect nutrients and sediments from in-flowing waters. With time, algae levels increase, and water visibility and depth decreases. Eventually, most lakes will become sufficiently shallow to form wetlands.

Human activities can greatly accelerate the natural process of lake aging by causing a rapid influx of nutrients and sediments. Common sources of these nutrients and sediments are storm water runoff from developed areas, failing septic systems, overuse of fertilizers, logging, and improperly-managed construction activities and agricultural practices. The influx of nutrients can produce explosive algae population growths, called "blooms", resulting in reduced water quality and unpleasant, smelly scum. It can also lead to an overabundance of aquatic plants, which can deplete the oxygen supply in the water and therefore degrade fish habitat, and limit human recreational uses. 

Regardless of the age of the lake or pond, aquatic plants serve many important functions. These include:

Stabilizing shorelines:
The roots of many aquatic plants, particularly emergent plants (those growing in standing water with much of their growth above the water), reinforce shorelines and protect soil against erosion from wind and wave action, boating wakes, currents, and other forces.

Providing habitat:
Many aquatic plants provide cover, food, nesting sites, and resting areas for fish, amphibians, invertebrates, birds, and mammals. Settings with a diversity of native aquatic plants will attract a variety of native animal species.

Resisting invasion by non-native plants:
A healthy native aquatic plant community will resist the establishment of invasive non-native plants, and often prevent them from becoming a serious problem.

Reducing nutrients:
Aquatic plants tend to bind up nutrients, leaving less available for algae and making algae blooms less likely. Emergent plants also slow water movement along shorelines, causing nutrient- laden sediment to settle to the bottom, where it is less available to algae.

Providing shade:
Aquatic plants, particularly those with floating leaves, create shade below their leaves. This restricts algal growth to open areas where light is available. The shade also reduces water temperature, which allows more oxygen to dissolve in the water, making the water more hospitable to animals that use dissolved oxygen (such as fish).

Producing oxygen:
As a by-product of photosynthesis, aquatic plants release oxygen into the water. This is important to fish and other aquatic organisms that depend on dissolved oxygen to survive.

While many landowners are interested in establishing native aquatic plant communities in and around their lakes or ponds, some property owners may be more concerned with controlling aquatic plants, particularly if the plants are non- native or are creating problems.

Aquatic plant management should take into account all of a lake's users. Not only are lakes important to people for reasons ranging from aesthetics to recreation, but there are other lake dwellers to consider: fish, amphibians, and other aquatic organisms, plus the birds and other wildlife that depend on a healthy lake. In addition, downstream residents and resources are impacted by the quality and quantity of water flowing out of the lake.

The most effective long-term control of problem aquatic plants will include efforts to control the sediments and nutrients entering the lake. Certain practices should be encouraged, including landscaping with native vegetation to reduce and filter runoff, and properly maintaining septic systems to prevent nutrient-rich effluent from leaching into the lake. Contaminants such as used motor oil, car washing detergents, and soil from landscaping projects should be kept out of storm water draining into the lake. Fertilizers and pesticides should be kept out of the lake by planting native vegetation and by using few or no garden chemicals.

Before you begin using any aquatic plant control technique, salvaging desired plants from a lake or wetland, or placing desired plants into a lake or wetland, consult with the Washington Department of Ecology and your county or city government. Many jurisdictions have regulations that limit or prohibit removing plants from or adding plants to wetlands or lakes. Because these regulations were designed to protect habitat and water quality, they usually have exceptions or allow one to obtain a permit for changes that will actually improve habitat and water quality. You will save yourself a lot of headaches (and possibly money) if you check first and get all of the required permits.