Biological Lake Weed Control

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Biological lake weed control involves introducing a species into the lake to destroy the weeds. At the present, there are only a few biological controls available to the lake manager, and they have their drawbacks. Biological controls are popular because they do not involve chemicals, and are perceived as being “earth friendly”, but this may not in fact be the case.

Problems with biological lake weed control

Remember, that the need for the control is probably because a non native species was introduced into the mix to begin with, introducing another to control the first hardly seems wise.

In cases where the “grass carp” has been introduced into environments other than it’s native habitat, the results have been mixed, ranging from achieving the desired control, to lakes completely devoid of vegetation and almost all other forms of aquatic life. Other issues are escape, which can produce disastrous results downstream, and the potential for the accidental release of non sterile, reproductive capable grass carp into the environment.

There are a few other biological controls available. Basically, these are “bugs” that dine on specific species. The same issues exist with them as with the grass carp.

In general, we do not recommend the use of biological control measures for these reasons.

A better form of biological lake weed control

Natural, native biological control can be used safely by simply following good cultural practices for your pond or lake. This simply involves providing for proper pH, proper fertility, and then allowing nature to do the rest. A properly fertilized pond or lake will produce the right amount of phytoplankton to keep the water tinted, and the weeds at bay, as well as producing healthy fish.

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