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Aquatic plants growing in ponds and lakes are beneficial for fish and wildlife. They provide food, dissolved oxygen, and spawning and nesting habitat for fish and waterfowl. Aquatic plants can trap excessive nutrients and detoxify chemicals.

However, dense growths (over 25 percent of the surface area) of algae and other water plants can seriously interfere with pond recreation and threaten aquatic life. Water plants can restrict swimming, boating, fishing, and other water sports. Water plants can impart unpleasant taste (musty flavor), decaying vegetation emits offensive odors (rotten egg smell), and algae can discolor pond waters. Dense growths of plants can cause night time oxygen depletion and fish kills. Green plants produce oxygen in sunlight, but they consume oxygen at night. Decomposing water weeds can deplete the oxygen supply, resulting in fish kills from suffocation. Dense plant growths can provide too much cover, preventing predation, and leading to stunted (small-sized) sportfish populations.

Prevention and Watershed Management:  Prevention is the best way to reduce aquatic plant problems. It is cheaper and easier to prevent weed growth than to control weeds in your pond. Constructing ponds with steep slopes that drop quickly into deep water can prevent weeds from rooting. Soil erosion and fertilizer runoff (including livestock wastes) are the two major causes of water weeds. Soil erosion magnifies the weed problems. Eroded soil particles not only make the pond shallower and allow rooted weeds to quickly invade, but soil particles also transport fertilizer (absorbed nitrogen and phosphorus) that further stimulates weed growth.

Aquatic Plant Control Methods:  Selection of the best treatment or combination of treatments depends on the species of water plant, the extent of the problem, economic considerations, local environmental conditions, and pond uses. First, be sure that you have an aquatic plant problem. Some aquatic plant growths are minor and temporary, and do not require costly weed control actions, thereby saving you worry, time, and money. If aquatic plants cover more than 25% of the pond surface area, you should consider implementing weed control. Second, different types of weeds (algae, floating-leaf weeds, emergent weeds, and submersed weeds) require different treatments.

Harvesting:  Physical removal of waterweeds from ponds is a good control technique. Harvesting of aquatic plants consists of three essential steps. These are (1) cutting or uprooting the weeds, (2) collecting the cut weeds, and (3) removing the weeds from the pond. Harvesting can be accomplished with simple hand tools and physical labor. Whole plant removal generally is better than cutting because some plants can reproduce from cuttings.

Shading and Chemical Dyes:  Commercially available nontoxic water dyes (nigrosine, analine, and aqua-shade) can be used to color the water in order to reduce light penetration and shade out nuisance plants. To be effective, the dyes must persist for several weeks. For the best results, this technique should be used in early spring at the start of the growing season before the waterweeds have had a chance to establish themselves. 

Biological Controls:  Introducing animals and plants that eat or compete with waterweeds represents another control method. Herbivorous animals (those that eat plants) include a wide variety of turtles, grass

carp, ducks, geese, and swans which can be stocked in ponds to consume aquatic plants.

Chemical Control:  Herbicides are commonly used to manage land and water plants. They should, however, be the control of last resort. Herbicides are relatively easy to apply and may be the only practical method of control in some situations. However, the treatment of weed-infested waters with herbicides must be used with caution. Herbicides can be toxic to fish and other aquatic life.

When using herbicides, treat one-third (or less) of the pond at a time to allow fish freedom to move to untreated, oxygen-rich areas of the pond or lake. Apply herbicides during the spring when water temperatures are cooler and dissolved oxygen levels are higher than in summer. Some herbicides are not as toxic at colder temperatures. Apply in early spring when weeds are small and not well established, and when fewer weeds are present to decompose.

Application rates should be according to the label and directions should be followed.

Applying the right amount of herbicide is especially important to achieve good control, avoid non-target toxicity, eliminate unnecessary expense, and comply with the legal requirements. After application of a herbicide, comply with the required waiting period before using water for irrigation, livestock watering, swimming, or fishing.

If interested in using a herbicide, please contact the office so the correct herbicide can be identified for your weed problem.