Lake Weed Control: The Best Method

The best lake weed control is smart cultural practices

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  • The best lake weed control is not aquatic herbicides or lake weed killers.
  • The best lake weed control is not with mechanical harvesting devices or lake weed cutters.
  • The best lake weed control is not with hand cutters and rakes.
  • The best lake weed control is not with biological controls like Asian fish and strange foreign beetles.

Lake weed prevention

The very best lake weed control is to never give them a chance to become a problem in the first place! The best lake weed control, like the best disease control, or the best fire control, is prevention!

How do you prevent lake weeds? Simple, do not give them a start, and do not give them a place to start. If you never allow the introduction of exotic lake weeds, you will never have an exotic lake weed problem. Other types of lake weeds may grow naturally in your area, and that is where the “not giving them a place to start” part comes in. I am not talking about getting rid of your pond or lake, but about getting rid of the conditions which favor a lake weed control disaster.

Lake, lake weeds, lake environment

For any organism to take hold, it must first have a host, and second, a proper environment. If the environment is unfavorable, or no organism or host present, the chance of having a serious problem is just not present either. Think of your pond or lake as the host, lake weeds as the organism, and the condition of your pond as the environment. Obviously you don’t want to do away with the host, that is your lake. The organism, that is, the lake weeds are ever present, so you can’t do much about that, the only thing left is to deal with the environment, that is, the conditions of the pond or lake.

Modify the lake environment

Your goal as a pond or lake manager practicing preventive lake weed control, is to modify the lakes environment to favor the health of the lake, and to help it to become resistant to the invading weeds. This is done by using good cultural practices.

Lake fertility

Lake weed control problems are a result of one of two things. Either the lake is overly fertile, and the weeds emerge as a result of the excessive fertility, or the lake is under fertilized, and the weeds grow as a result of the lake beds exposure to sunlight. In both cases, shallow water is usually a factor. Fertility, out of balance, is always a potential problem. In the majority of cases, lack of fertility is the problem.

Why is this? When sunlight reaches the bed of a pond or lake, it warms the soil, and activates photosynthesis in plant life existing in a more or less dormant stage. This encourages growth. If sunlight does not reach the bottom, growth is prevented. Pond fertility, when in balance, produces phytoplankton which shades the bottom by coloring the water.

To solve the lake weed problem, to prevent it from recurring, the fertility must be kept in balance. Monitoring and maintaining lake fertility is the primary tool for lake weed prevention.

See also: How To Fertilize A Pond Or Lake

Why Aquatic Weeds And Filamentous Algae Occur


This is the basic sequence of events leading up to pond scum and lake weed problems. It should be noted that not all problems arise from these causes. There are problems related to the over fertilization of a body of water which can lead to some of the same results. There are tell tale signs which can be easily seen by checking water clarity. If the water is a virtual soup of green suspended algae, the water is too fertile, and other measures, like adding vegetation to the intake side to filter some of the nutrients should be taken. While this does happen, it occurs so infrequently that I have seen only one or two cases in my life. Sequence of events resulting in pond scum and lake weed problems:
  • There is not enough fertility
  • Water becomes too clear
  • Sunlight penetrates to the bottom
  • Sunlight warms the bottom
  • Weed and algae germination and growth is initiated
  • Weeds quickly grow through the water profile
  • Filamentous algae begins to rise from the bottom
  • Weeds and pond scum become the dominate feature of the lake or pond
  • Fishing and recreational use becomes difficult
  • Mosquitoes arrive and decide they like the surroundings
  • Water quality worsens
  • Dissolved oxygen is low in the evenings
  • Fish rise to the top to gulp oxygen close to the surface
  • Without plankton, the life cycle is slowed and the fish become hungry and skinny
The last problem listed in this sequence has probably been a problem for a while. Phytoplankton is needed in the water to:

Color the water for sunlight control

By coloring the pond or lake water, sunlight is prevented from reaching the lake bed where weeds and filamentous algae get their start. This provides lake weed and pond scum prevention.

Shade the water for heat control

By shading the water, the temperatures are moderated, providing better, more comfortable conditions for aquatic life.

Produce oxygen throughout the water profile

With higher oxygen production in the water, fish are able to breathe easy, and concentrate on avoiding predation, and food intake.

Provide food for the life chain

Because phytoplankton is the beginning of the "circle of life", food for fish is produced as a natural result. Producing phytoplankton, or algae bloom is pretty easy to do, but there are a few preliminaries. You can read more about them: Pond Scum Prevention Pond Algae

Pond Scum And Lake Weeds

Part 2 in our series on lake and pond interaction

Pond scum control


Most of the questions regarding pond scum, lake moss, or pond algae ask how to get rid of it. This is perfectly logical. The problem is, that the pond scum itself  is just a symptom of other problems. The first evidence we have of it’s existence is when it floats to the top and interferes with the aesthetics, our recreation or our fishing. Filamentous algae, or pond scum as it is more commonly known exists in most bodies of water, and will begin to show itself when conditions are right for it. It grows from the bottom, and sunlight allows photosynthesis when it penetrates to the bottom. The photosynthesis process allows the algae to take in carbon dioxide, and exhale oxygen, some of the oxygen, which is good for fish, will be released under the algae mat, and gradually cause it to float to the top, where it becomes a nuisance.

Lake weed control

Most of the questions we receive about lake weeds revolve around how to get rid of them. As with pond scum, most lake weeds get their start at the bottom of the pond when sunlight reaches them. When conditions are right, they may grow out of control causing problems for the pond owner. Some aquatic weeds are capable of doubling in mass in a week or less, leaving the pond owner with a huge aquatic weed control problem. If measures are taken to kill the weeds with aquatic herbicides, the weeds will die, and drop to the bottom where they will decay over time. This can produce a slimy, and high organic fertility on the pond bottom, perfect to supply nutrients to the next generation of weeds!

Mechanical lake weed control

Mechanical controls and mechanical lake weed harvesting may produce less slime at the bottom, but care must be taken when using a lake weed cutter to collect all the fragments, as aquatic weeds are notorious for their ability to reproduce from fragments. One plant chopped into 100 pieces may turn into 50 new plants in a matter of days. See: The relationship between excessive aquatic vegetation, Mosquitoes And Skinny Fish

Lake Weed Killer: Aquatic Herbicides

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Lake weed killer

What is the best lake weed killer? That depends on a lot of things, including the type of weed, the stage at which the weed is discovered, the water and weather conditions, and local laws and ordinances to name a few. Choosing aquatic herbicides can be a little difficult, so we thought we would offer a few general thinking points.

Pond weed types

To determine the type of weed, you should determine if the plant is an algae, a floating plant, a submerged plant, or an emergent plant. Each type could require different aquatic herbicides. If the weed is primarily underwater, it is likely submerged. If the lake weed looks like a lily pad, it is probably floating, if it is growing straight up from the shallows, it is likely an emergent plant. The various types of algae may be more difficult to identify as algae, since some, like skunkweed, also known as musckgrass and chara, bare a striking resemblance to other plant types. Please note that these classes are merely for the purpose of identification, and may not follow strict definitions. A submerged plant may become emergent, and vice versa. There is an excellent tool for lake weed identification called “Aquaplant“, which can help in the identification process, as well as deciding upon treatment options.

The weed should be identified. Discovering the type of weed will help you to identify the weed, and the best aquatic herbicides to use.

Stage of growth

What is the offending plants stage of growth? Youthful weeds are easier to kill than older hardened weeds. This is known as the juvenileity factor, and may effect the amount of chemical, or even the type of chemical to be used as a lake weed killer.

Water conditions

If the water is muddy or turbid, it will have an effect on the lake weed killer. Most aquatic weed killers are designed to be neutralized by soil particles. Muddy water may require the aquatic plant manager to eliminate the source of the turbidity, and “flock” the water to allow the suspended soil particles to drop to the bottom before proceeding with the use of  aquatic herbicides or pond weed killer. Under conditions where turbidity cannot be completely controlled, the use of the most desirable chemical may be sidelined in favor of another chemical which works better under such conditions.

Weather conditions

Weather conditions may cause one aquatic herbicide to be less desirable than another. The use of 2-4d on a hot still day may not be wise. The chemical can volatilize under certain circumstances, and end up damaging nearby vegetation. Large quantities of rain may dilute some chemical products, while others may work well under such conditions.

Lake weed killer types

For our purposes, aquatic herbicides fall into 2 categories:

Contact aquatic weed killer

A contact type aquatic weed killer kills only the part of the plant that it comes in contact with. In many cases, this is sufficient, especially if good management practices are used when following up the treatment. See: Lake Weed Prevention Advice for follow up advice.

Systemic aquatic weed killer

A systemic lake weed killer, when properly applied, kills the plant all the way to the root. Systemic aquatic herbicides can be an advantage in some situations, particularly in shallow areas where proper management may be difficult to achieve due to lack of depth. Systemic herbicides tend to have a longer effect on aquatic weeds.

Laws and ordinances

Some aquatic herbicides may have label restrictions which could preclude their use in your situation. Some may be bound by state or local ordinances. It is always best to do your homework, and do it well before using a lake weed killer.

Lake weed control: Prevention

The most important aspect of pond weed control is what you do after using an aquatic weed killer. If conditions are not altered to reduce the amount of sunlight reaching the lake bottom, the lake weed problem will return. This may involve making the water deeper by dredging, raising the water level, or producing algae bloom to tint the water. Learn more about lake weed prevention See: Lake Weed Prevention Advice

Lake Weed Control Advice


Aquatic weed control can be practiced in several ways, of which, the very best is lake weed prevention. Chemical control relies on herbicides to accomplish the job of vegetation control. Mechanical aquatic vegetation control is the act of physical weed removal, and is used generically for almost any time of physical lake weed control such as mowing, or rolling the vegetation. Biological lake weed control is accomplished by introducing a living predator into the pond or lake. These are limited at this time to a very few, including grass carp, and a few insects. As we said, prevention is the best method, and the follow up process is important for preventing future invasions.

Lake weed prevention.

Prevention is the best from of control for any problem, ever. However, there are times when prevention may not have been an option, and for such cases, exercising control, or practicing management is the only recourse.

Chemical lake weed control

Chemical aquatic weed control is often seen as being the least acceptable form of aquatic weed control due to environmental concerns. These concerns are largely unfounded. The amount of chemical that can legally be used is most often measured in parts per million, and relatively few parts per million at that. The chemicals used have been thoroughly tested, and while most of us have a healthy distrust of both government agencies and chemical manufacturers, I believe that in this case, they have earned our trust. The chemicals that are used for aquatic vegetation control are low dose, low toxicity, and lose their toxicity quickly in lake and pond water. You probably get more parts per million of pharmaceuticals in your drinking water than the allowable amounts of weed killers in fish ponds!

Chemical applications and "fish kill"

Occasionally we hear of someone treating a pond or lake and killing all the fish. This is a rarity, but it has happened. In all cases of which I am aware, the chemicals played only an indirect part in the problem to the extent that the chemicals did what they were designed to do but the lake manager killed off too much vegetation at one time, and the rotting vegetation used all the available oxygen, the fish died of oxygen depletion. Don't be afraid of chemical lake weed killers, just be certain that you use them properly.

Mechanical lake weed control

Mechanical aquatic weed control can be a good way to control aquatic weeds, but like other methods, it comes with a price tag.  It is usually a last ditch effort which will result in the continued need of the process.

Lake weed reproduction and fragmentation

Aggressive aquatic weeds like Hydrilla can reproduce from vegetation fragments  at a rate of  50 percent or more. This means that if your mechanical harvesting method shatters the weed into 200 pieces, and only 100 of the pieces are retrieved, you will have created about fifty more new plants! The trick to effective mechanical lake or pond weed control is to cause as little fragmentation as possible, and collect all the fragments. Machines with serious vibration, or machines that tear, rip or shred weeds should be avoided unless you are willing to seine the lake completely a time or two.

Mechanical weed control equipment

There are a few pieces of equipment I can recommend if this is the route that you intend to try. Email me for the details. Just beware that a commitment to mowing your pond or lake once, probably translates into the need to mow your pond or lake on a regular basis just as you mow your lawn.

Biological lake weed control

Biological aquatic weed control is one of the most difficult control measures to get right. The few biological methods for weed control come with a caution. Biological controls of this type usually require the introduction of a new species into the habitat. This would normally be one of the predators from the same location as the weeds you are attempting to rid yourself of. You will then have 2 exotic species in the habitat! There are many control measures exercised before the approval of a biological control, and they work pretty well under normal circumstances, but nothing in nature is static, and serious consequences are a possibility. As of this time, biological aquatic weed control seems to be limited to one oriental fish, and a few insects.

Lake vegetation control follow up

Please be aware, that any of these treatment methods are only effective for the amount of time that it takes the weeds to regain their growth unless something else is done. Action must be taken to prevent sunlight from reaching the bottom of the lake to prevent regrowth. If these measures are not used, and the proper steps are not taken, the problem will return! For information on pond scum prevention and control see: Pond Scum Control Advice For a paid consultation about dealing with your aquatic weed and pond scum problem see:

Lake Consultation

Lake Weed Prevention Advice


Lake and pond managers and owners spend a good deal of time and money dealing with lake weeds. In fact, it is fair to say, that dealing with aquatic weeds is where the lions share of pond and lake management time and money is spent.

Exotic lake weeds

Lake weeds are an ever increasing problem today, in large part, because of the presence of so many exotic weeds, and their amazing and terrible growth habits in our climate. A plant that may have been a beautiful and productive part of it's native landscape in another region of the world can become a destructive lake eating monster when transplanted into a new environment. Unfortunately that is what we are experiencing in the Southern United States.

Native lake weeds

As bad and difficult to deal with as exotic lake weeds are, they are not the only weed problem that lake managers deal with. Our native varieties can be devastating if conditions exist which encourage their excessive growth. Native aquatic weeds can become almost as problematic as exotic aquatic weeds.

Preventing lake weeds

Lake weed control can be difficult and expensive. Every treatment option has it's drawbacks, some are like the medications advertised on television that have side effects worse than the original problem. In fact, there are no good or great treatment options, because they all deal with the symptoms and not the problem. There is a better way. When dealing with lake weeds, we can think of the process as a series of steps, with the best options at the beginning, and the least desirable options left to the end as a fall back position. The best option is prevention. Stopping lake weeds before they get a start is better than dealing with lake weeds after they have become a problem, in the same way that avoiding auto accidents and house fires is better than the very best methods of dealing with the aftermath. Prevention is always better than treatment.

Keeping lake weeds out

It is obvious that if there are no invasive lake weeds introduced into the lake, there will be no problem with them. So how do the lake weeds get into the lake to begin with?

Natural elements you can't do much about

The processes that bring invasive lake weeds into a body of water can be natural, such as birds and animals, or overflow from infested ponds or lakes upstream. This can be unpredictable, and unpreventable, but luckily, this is not the most common means of aquatic weed trans-location.

Human elements you can do something about

By far, the most common means of aquatic weed movement is human beings. This is usually done with boats that have not been cleaned properly after visiting another lake, or fishing equipment that has small pieces of plants that go unnoticed, and even by recreational equipment like all terrain vehicles. If living tissue from some exotic lake weeds from any source makes it's way into your lake or pond, it can, and probably will start to grow, and that growth may be geometric! If you are ever going to become an advocate of clinical cleanliness, this is the place to do it! Check everything that goes in or near the water. Leave no stone unturned when it comes to clean up, check live wells, bilge, propellars, everything! Check lures, nets and anything else that might hold a fragment, because a fragment of some exotic lake weeds can become a lake full  in just a few weeks!

Proactive lake weed prevention

The next step has elements of both treatment and prevention. It involves making your lake less vulnerable to lake weed infestation by strengthening it's defenses. Ideally, your lake or pond should have no areas under 3 feet in depth. This depth will control the majority of the lake weeds we consider problematic. In 3 feet of water, it is difficult for light to reach the bottom, and that is where most weed problems begin Unfortunately, most ponds and lakes are just not built this way, and even if they were, sediment gradually accumulates around the edges. Raising the water level can be unsafe if the dam is not strong enough and high enough to hold, and dredging can be very expensive. Whether you have shallow spots or not, there is another approach that you should consider, in fact, this should be done whether you have problems with lake weeds or not.

Water color

If your lake has clear water to a depth of more than 24 inches, your fish are probably hungry, and you probably have a problem with lake weeds and pond scum. Tinting the water will prevent the sunlight from penetrating to the bottom, and will, thereby, prevent the majority of submersed, and emergent lake weeds. How you tint the water will determine whether or not you have skinny fish!

Algae bloom

There are colorants on the market that do a good job of preventing light. They serve a useful purpose in many cases, but not when it comes to ponds and lakes used for recreational fishing. In such cases, what is needed is plankton, or non connected single cell algae. Plankton is the natural colorant for ponds and lakes, and it is the natural food for the microscopic aquatic life which feed the bugs, which feed your fish. Algae bloom is the beginning of the life cycle in lakes. The great thing about this is that it is easy to produce. If all other conditions are right, a relatively small amount of fertilizer can start the process in a matter of days, or even hours. For lake weed control methods see: Lake Weed Control Advice For a paid consultation about dealing with your pond scum problem see:

Lake Consultation