Lake Fertilization

Pond management and lake fertilization

There are times in the life of a pond or lake when clearing the water may be necessary. At those times, there are flocking agents that will do the job well. You should be aware however, that a completely clear pond or lake is not the optimum circumstance for a healthy body of water. Unfortunately, there are many who suffer from the illusion of healthy happy fish in a beautiful crystal clear pond, but it is just that, an illusion! For healthy fish, and for a healthy pond ecosystem, there must be something growing in the water, and that something is phytoplankton. The way to get it is through fertilization.

Nowhere in the world of living things can the effects of fertilization be seen more clearly than in a pond or lake. The effect can be almost immediate, and often drastic. The results, if properly implemented, will be a near incredible increase in fish size and numbers. Properly timed and implemented fertilizer applications will also reduce the population of unwanted submersed and emergent weeds.

An analogy: Cattle pastures and fish ponds

Think of it in terms of a cattle pasture. If you fertilize the grass, the cattle will grow more quickly, and the pasture may be able to support more cows. Reproduction will increase, and pounds of milk or beef per acre will increase. Lake fertilization works the same way. Increased pond fertility will increase the food source for your fish, which will increase their size and numbers. If done properly, you will also cause the grasses to outgrow the weeds.

What kind of fertilizer and how much

Fertilization will produce algae bloom, or phytoplankton in your pond. The right fertilizer is a fertilizer high in phosphorous and low in the other 2 elements. Phosphorous is the middle number in the 3 numbers listed on a bag of fertilizer. You need to add 40 lbs of 20% phosphorous, or 20 lbs of 40% phosphorous, or something similar in ratio per acre to initiate algae bloom. It takes about 4 to 8 pounds of pure phosphorous to produce or maintain algae bloom in an acre of water. If you had a product with 80% active ingredient, you would need about 10 pounds. However you get there, you need about 8 pounds of the second number in the fertilizer label, and as little of the other ingredients as possible.

There are some great pond and lake fertilizers available, but if you can’t find them, regular old high phosphorous agricultural fertilizer granules can be used. There are also liquids available, but when using liquids in a pond or lake, always remember that the fertilizer is heavier than the pond water, and will sink to the bottom unless you add water before releasing it into the pond water.

An alternative to phosphorous for pond fertilization

With phosphorous being closely monitored today, and restrictions on the horizon, it may be a good idea to look into alternatives such as the ones mentioned in this post by Mr. Bhaskar on our Lake Advice Blog: Diatom Algae. For the details on various methods fertilize your pond see Pond Fertilization Methods . Find more information about the effects of lake fertilization throughout this site.

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 Lake Weeds Mosquitoes And Skinny Fish

Part 1 in our series on pond and lake interaction

The common thread in common lake problems


Controlling pond scum, lake weeds and mosquitoes and raising healthy fish may seem complex and difficult. There is no miracle cure, there is no magic bullet. There are no products on the market which will get rid of your pond scum or lake weed problems, prevent them from returning, and leave you with a healthy pond or lake in the process. Even such biological controls as grass carp have problems that will leave you with even bigger problems than the ones you started with. If all of this makes the situation seem a little bit hopeless, don't lose heart, it is not. Some things are not as simple as they seem. Most people would see pond scum, lake weeds, mosquitoes, and skinny fish as unrelated problems. The fact is, that they are all entwined, and at the root of these problems, is one problem with a seemingly strange, but simple solution!

Lake management looking at the big picture

We took a long look at the questions we receive, and realize that most of them have to do with specific issues, and that they show a common misunderstanding about pond and lake management. They seem to show that many pond owners don't understand how all the parts of a pond or lake interact. Our most common questions revolve around the issue of pond scum, and lake weeds. This is followed by questions which revolve around mosquito control, and poor fishing conditions, and what has been termed “skinny fish”. These issues are commonly addressed as individual issues, when in reality, they all have the same root cause. What we would like to do is show the big picture of how a lake with one thing wrong, probably has several problems, and one main problem which all the others revolve around. See: Pond Scum And Lake Weeds

Pond Scum Prevention Pond Algae

Pond Scum Prevention Pond Algae


We are all aware that pond scum may be the secret of the fuel production of the future, but in the mean time, it is probably not something you want in your recreational fishing pond. For one thing, it is ugly, for another, it is often stinky, and to make matters worse, it can do harm to other forms of aquatic life, and harbor potential disease carriers like mosquitoes. Not all algae is bad, but an abundance of blanket weed pond scum, almost always has an adverse effect on aquatic life. You can find the proper distinction between the filamentous pond algae that plagues pond owners, and the types of algae necessary to maintain healthy pond life below.

What causes pond algae?

Algae is always present, but what causes it to spring up in such dramatic fashion in the spring and summer? The best answer is sunlight. Pond algae starts in the bottom of a body of water, in spite of how it may appear. The floating mass you see at the top of the pond is algae that started on the bottom, and gained buoyancy as it took on air, and floated to the top in the stinky familiar mass. Sunlight penetrating to the bottom of a pond starts the photosynthesis process, and kick starts the whole nasty mess.

Different types of pond algae

So, is all algae bad? The answer is a resounding NO! In fact, the best means of preventing pond scum, or filamentous algae, is by producing another type of algae. Plankton. This single cell algae will remain suspended in water, providing food for the tiny animals that provide food for the larger life forms, which in turn, provide food for your fish, and, if you are a successful angler, food for you.

Pond algae control using algae

Not only does this type of algae feed the fish, it also colors the water. That nice green or blue green tint that you see in healthy ponds and lakes is suspended algae, and one of the best services it provides is tinting the water, thereby preventing sunlight from reaching the bottom of the lake or pond, preventing the growth of unwanted vegetation, and providing pond algae control. Yes, pond scum, like most aquatic plant life, gets it's start at the bottom of the pond, and as it gains oxygen, it floats to the top where it produces all sorts of undesirable conditions, like the ones mentioned above, and including lousy fishing conditions, oxygen deprived fish, and frustration.

Algae for tinting the water

Getting rid of the pond scum type of pond algae can be a difficult task, and if the conditions that allowed it are not changed, it will return. Remember, the problem is sunlight reaching the bottom of the pond, so something must be done to prevent it from doing so. This could include raising the water level, which may not be possible in all cases, dredging or otherwise making the lake deeper, or coloring the water. The last, is usually the chosen option. There are dyes which can color the water, but, if fish production is what you desire, remember that dyes do not feed the fish. In small ponds for catfish production, where regular feedings occur, this may work, but where no feeding takes place, or where other types of fish are desired, dyes are not the answer. Once again, plankton is needed to continue the life chain, and prevent the pond scum problem.

How to produce plankton to prevent pond algae

So, how do we produce this plankton? The answer is simple: Fertilize the pond. Now before you start thinking that it is a crazy idea, let me do a little explaining. Fertilizer, usually a fertilizer high in phosphorous, will encourage algae production through a process known as algae bloom, and this will produce the coloring needed to stop pond scum. There are a few things you need to check before you fertilize.
  • First, get rid of the existing pond scum, and give it time to decompose.
  • Second, test the water pH. Anything lower than 6.8, and you need lime to raise the pH. Something between 6.8, and 8.6 is ideal. If it needs correcting, correct it before proceeding.
  • Third, check the secchi depth. It should be between 18 and 24 inches. If the secchi depth is less than 18 inches, there is another problem. If it is more than 24, begin fertilizing as soon as possible, and continue the process throughout the summer, or until the depth is less than 18 inches.

Other factors

There are other factors, like muddy water, which will need to be solved before pond algae treatment, and you will need to know the details like how to use a secchi disk, and how much fertilizer, which are covered in other places on this website. See: How To Fertilize A Pond Or Lake Note: Filamentous algae goes by many common names: Pond algae, pond scum, pond slime, pond blanket weed, string algae, and others. There are other types of algae present in many ponds, some of them are beneficial to the ongoing health of the pond. Chief among these is the algae known as phytoplankton or simply plankton, the simple single cell algae that is suspended in water, and produces food for the life chain.

Lake Advice And Consultation


Lake Advice is an advice and consultation service for property owners who have pond and lake problems, from an experienced pond and lake manager, and lake weed control specialist. We offer basic pond and lake care information on the website, and consultation via phone and email.

Why are we offering this service?

There are many reasons. We have found that pond and lake owners, like everyone else, want to spend as little money as possible on maintaining their lakes and ponds. This is understandable and we respect this concern. Hiring a lake manager, or lake weed control specialist can be an expensive proposition.

The high price tag is a result of a combination of factors:

  • The high cost of chemicals and equipment used for lake management and lake weed control.
  • The difficulty of becoming a licensed aquatic vegetation manager.
  • The high cost of maintaining the license and insurance necessary for the job.
  • The limited numbers of available jobs in the market, and the uncertainty of when the next job will arrive forces a slightly higher labor cost.

There are factors that add to the degree of difficulty in this line of work:

The degree of uncertainty involved in practicing lake weed control when so many factors are beyond the control of the lake professional can be a problem. Weather factors, and human factors can negate the results of  a good application. The reluctance of many lake owners to perform the follow up needed to maintain the body of water after an application has been made can lead to problems as well. In many cases, the best proposal is for the property owners to perform the work for themselves. The advice offered on this site is for just such a situation. It should be remembered that the advice offered here is just basic advice. For more detailed help we offer online consultation for a reasonable fee.