Know Your Weeds To Help Your Fishing

Some aquatic weeds might help fishing, but many others can choke a pond to death. Here are four of the worst.

Mark Mongin | April 1, 2009


Aquatic weeds can form dense structures that block sunlight and reduce oxygen levels.

The Southeast is rich with ponds, lakes and wetlands that offer countless memories for anglers, swimmers and outdoor-water enthusiasts.

Ponds and lakes are more than places to wet a hook. They enhance the value of the rural landscape, and fresh water is critical for crops and habitat quality for a variety of wildlife. The demand for clean and open water suitable for use has increased with population growth and development.

Often, however, the ol’ fishing hole is just not what it used to be — grown shut with nuisance levels of aquatic weeds and algae.

So what happened? Increased activity in the watershed from land development or crop production can create water runoff which is rich with nutrients and organic sediment. This elevates nutrient and sediment levels in many ponds.

Higher nutrient and sediment levels increase the nitrogen and phosphorus content of the water. Combine this with the introduction of exotic or nuisance aquatic plants, and you have a major pond-management problem.

Increased nutrients, plus the introduction of exotic and nuisance plant species with abundant sunlight, will result in a disruption of the natural water-quality balance of many ponds and lakes.

The reason is because exotic aquatic plants and aggressive native species out-compete beneficial native vegetation, covering the surface of the water or filling the pond and lowering water quality. This may happen in one growing season!

So how do you prevent this invasion and protect your pond?

It starts by knowing what and how to identify the problem. Start early and survey your pond often for new weed growth. Here are four exotic and/or nuisance aquatic weeds to watch out for.


Duckweed, a small floating plant, is the No. 1 nuisance aquatic invader in the Southeast.

It has shoesole-shaped leaves with small, hair-like roots hanging below. It resembles a four-leaf clover and is approximately the size of a pencil eraser.

Once established, it can cover the entire water surface and resembles a golf-course green.

Duckweed in a beaver pond can be great for duck hunters, but in a pond or small lake it has explosive reproductive capacity and can cover the entire surface of the water.

It can cut off sunlight to submerged plants and can cut off oxygen to fish. Duckweed is a common nuisance aquatic weed spread from pond to pond via waterfowl or other wildlife.

While it is commonly mistaken for algae, duckweed is actually a tiny plant with an explosive reproductive capacity that can completely cover a pond in just a few weeks.

Many pond owners consider duckweed to be their toughest aquatic weed problem.

Fortunately, there are effective control options to manage duckweed. Carefully applied herbicides and improved aeration and water circulation are useful tools to reduce the nuisance level of this stubborn, unwanted aquatic plant.

Eurasian Watermilfoil

Native to Europe and Asia, this exotic was introduced into the United States in the 1940s as an aquarium plant.

This submersed, mat-forming perennial remains green during winter and survives throughout the Southeast. Eurasian watermilfoil is an aggressive invader of ponds and lakes. It starts growing early, getting the jump on our beneficial native aquatic plants here in the Southeast, forming dense mats that prevent light penetration. It can crowd out and destroy natural fish habitat provided by native plants.

The leaves of Eurasian watermilfoil look like feathers. There are other forms of native milfoil that do not get as dense and can be beneficial to a lake’s fishing productivity, so identification with the help of a professional is really important.

Eurasian watermilfoil is an aggressive aquatic weed invader and responsible for more habitat loss than any other submersed aquatic species in the Southeastern states.

Most commonly, it spreads when plant fragments hitch-hike on boats and trailers, but it also produces seeds. Eurasian watermilfoil leaves are feather-like and sometimes produce reddish flowers that extend above the water. The stems are red to brown in color. It can dominate a pond very quickly by fragmentation. Pieces of the plant grow roots to develop a new plant.

There are many native milfoil plants which do not have as many feather-like leaves and are much less aggressive.

Carefully planned herbicide applications can reduce infestations.

Curly-leaf Pondweed

Like Eurasian watermilfoil, curly-leaf pondweed is a non-native species that poses a significant threat to many freshwater aquatic environments.

As the name implies, the leaves of this plant are somewhat stiff and crinkled, approximately 1/2-inch wide and 2 to 3 inches long. Leaves are arranged alternately around the stem.

Curly-leaf is an active plant, growing early and aggressively until July or early August, and then dying off for the season.

The problem is curly-leaf dominates the pond, crowding out many other more beneficial aquatic plant species.

Each year this aggressive perennial will spread taking over more and more of the aquatic environment.

In the springtime, curly-leaf pondweed can form dense mats that may interfere with boating and other recreation on lakes. Curly-leaf also can cause ecological problems because it can displace native aquatic plants. In mid-summer, curly-leaf plants usually die resulting in rafts of dying plants piling up on shoreline.

Die-off of curlyleaf pondweed often is followed by an increase in the nutrient phosphorus and undesirable algal blooms. If left unmanaged, the bottom of the pond will accumulate high levels of organic matter or muck from years of build up and die off of curly-leaf pond­weed.


Unlike most of the other bad weeds that can take over a pond in the South­east, coontail is native to the United States and is not an exotic invader.

Although native, coontail is capable of growing to nuisance levels when left unmanaged in an area with plenty of nutrient-rich habitat to grow in. Mucky, still, shallow ponds are particularly vulnerable to this plant, which has the potential to keep growing until it completely takes over and fills up a pond.

Coontail is a submerged aquatic plant that can be easily identified by the “raccoon tail” cluster of leaves at the end of the main stalk.

It has slender stems and leather-like leaves. Coontail is called hornwort when sold for aquarium decorations. It spreads into ponds after aquariums are dumped into ponds and lakes.

Coontail is easily managed with carefully planned herbicide applications, which have been proven effective at reducing infestations.

For more information on how to identify these problem plants and the best management practices to control weeds that could cause major problems in our Southeast ponds and lakes, contact SePRO Corporation’s Mark S. Mongin at 11550 North Meridian Street, Suite 600, Carmel, Ind. 46032-4565 or by phone at (866) 869 8521 (toll free). Check out their website at

Aquatic weeds can form dense structures that block sunlight and reduce oxygen levels.

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