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

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