How Can I Prevent Pond Algae?

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Not all algae is bad First, let's get our minds wrapped around this: Not all algea in ponds and lakes is bad. The problem comes when you have too much algae, or the wrong type of algae. In fact, the best treatment for pond algae, is algae! I know it sounds a little strange, but that is the way it works. What is pond algae When most people think of pond algae, they think of the type of algae commonly called pond scum, or blanket weed. The proper name for it is fillamentous algae. This is a type of algae that forms long fillaments or strings that then mat together to form a blanket on the surface of the water. This mat or blanket of algae makes fishing, boating, and other recreational use of a lake or pond difficult and distastefull. Pond scum also allows a perfect environment for mosquito production. In general, blanket weed in a lake is not a good thing for human use and interaction with the lake. Understanding pond algae To understand the best treatment for it, we need to understand where it starts, and how it starts. When we notice pond scum, we notice it on the top of the water, but that is not where it begins. Fillamentous algae starts at the bottom of your reservoir, and rises through the water profile as it gains bouyancy from the oxygen it produces. Eventually, enough oxygen is produced to lift it to the top of the water where it floats annoyingly. Clear water is the problem The problem is not that your pond or lake water is too murky, the proble m is that it is too clear. Again, I know that this is counter intuative, but bare with me. You have probably heard someone say "I can't see through muddy water." when they wanted you to move out of their line of site. The same principle applies here, because light penetrates straight through clear water, and because sunlight is needed for plant production, if the water is not clear, plant production is limited. If your water is too clear, you will have pond algae. The answer is not to go out and make the water muddy, the answer is to produce a single cell algae known as phytoplankton to tint the water, and prevent sunlight from reaching the bottom. So how do we prevent pond algae? Pond fertility is the answer. Check your pond or lakes water. If it is clear to a depth of more than 20 inches or so, it is too clear, and chances are, your fish are going hungry as well. A good fertilization program will solve both problems, and many others as well. This is how it works: When the proper amount of the proper fertilizer is introduced into the water, in the proper way, the single cell algae known as phytoplankton will reproduce rapidly in a process called algae bloom. This will continue as long as the water is fertile. The green color, or the golden brown coloring that this method produces will tint the water, preventing sunlight penetration, and preventing the growth of fillamentous algae. To learn how to do this see these pages, How To Fertilize A Pond Or Lake Lake Fertilization Lake Management Lake Weed Control Water Depth Secchi Depth and all the posts in this section of Home And Garden Press: Lake Management

Barley Straw Pond Algae Control: How To


Barley straw can be an effective treatment for the prevention of blanket weed pond scum, pond algae, but there are a few caveats and precautions to keep in mind. Barley straw pond algae control is not always the best method of pond algae control. Read the list of precautions, and decide for yourself. Instructions on the use of barley straw pond algae control, including the proper methods are given below.

Barley straw will not:

  • Eliminate existing pond scum
  • Work in muddy water
  • Work in water with low oxygen
  • Work only against bad pond algae production

Barley straw will:

  • Decompose, adding nutrients to the water
  • Use oxygen during decomposition
  • Kill all forms of algae, including phytoplankton
Barley straw only works to prevent pond algae, not to kill it, and will not work in certain conditions like muddy water and low oxygen. It will decompose and use oxygen during the process which can be fatal to fish if too much decomposition occurs too quickly. Decomposition also produces nitrogen which can act as a fertilizer for future weeds and algae production, which will increase in the newly cleared water. Barley straw will decrease phytoplankton production resulting in water clarity, and a lack of food for fish as well as allowing sunlight to penetrate to the bottom, which can result in more pond algae and lake weed production after the barley is gone. A proper fertility program to promote the growth of phytoplankton should be put in place to prevent such an outcome. Once a good fertility program is in place and ongoing, the need for any pond algae treatment will evaporate in most cases.
With all of these possibilities in mind, this is the process you can use to apply barley straw to a pond or lake for the treatment of pond algae:

Amount of barley straw to use

If pond scum is a recurring problem, 100, to 250 pounds of barley straw per surface acres can be used for preventing unwanted lake algae. A surface acre, is 43,560 square feet. To determine the size of your pond or lakes surface area, multiply the number of feet from side to side, with the number of feet end to end. The numbers do not have to be precise, just as close as possible. If the ends or sides are not equal distances, simply average the distance of both sides, and the distance of both ends before multiplying. This should be close enough for a barley straw treatment.

How to apply barley straw

Separate the barley into equal units, and place it in weighted mesh bags, rolls of hardware cloth, or cages, and sink them around the pond. A string or rope tied to the bags and a stake will help in retrieval. 50 pound onion bags or gunny sacks work well, you can stuff about 6 to 8 pounds of barley straw in an onion bag or gunny sack.

Where to place barley straw

Barley straw will only be effective in oxygenated water, which limits placement to the edges and close to the surface, so do not submerge the straw more than a few inches below the surface or it will simply rot without producing the desired effect. See also: Using Barley Straw As A Blanket Weed Treatment and Barley Straw Pond Algae Treatment Drawbacks

Pond Scum And Lake Weeds The Real Problem

Part 4 in our series on lake and pond interactions

The real pond scum and lake weed problem


The problem is sunlight. You can’t do much about that. Specifically, the problem is sunlight reaching the pond bottom, which you can do something about! The common issue for pond scum and lake weeds is sunlight penetrating the water to the bottom of the pond or lake. When this happens, a process begins which will allow lake weeds to grow unchecked, pond scum to develop and start to rise to the top, and the secondary result will be mosquitoes, and even though the plants and algae will produce oxygen, they will at some point cause conditions which will deplete oxygen in the water, and all the while, your fish will be starving. All of this because sunlight reaches the pond bottom!

Preventing lake weeds and pond scum by preventing light penetration

There are a number of ways to prevent light from reaching a pond or lake bottom. You can raise the water level, lower the bottom through dredging, or color the water in some way. Raising the water level can produce good results in some cases, but may not be practical, and it still doesn’t deal with the issue of skinny fish. If the water is deep enough the sunlight cannot penetrate, but something needs to be done to feed the fish if the water is clear to a depth of more than 24 inches, so even if you can raise the water level, or dredge the shallow areas, more is needed. The water needs color to shade the bottom. This can be done with dyes and colorants, but, once again, you still have the issue of skinny fish. There is a product that can resolve both the light penetration issue, and the food supply issue.


Plankton is a single cell algae which is suspended in the water of healthy ponds and lakes. It provides oxygen to the water, food for the tiny invertebrates that feed the larger aquatic life, which ultimately feeds the fish in the lake, and provides color for the water helping to prevent the excessive growth of unwanted vegetation and pond scum. This is sometimes called algae bloom.

Producing algae bloom

The reason that plankton does not grow in a pond or lake is lack of fertility. The solution to this problem is to add fertilizer. To learn more about this process see: pond scum prevention and Lake weed prevention Pond scum is filamentous algae, and is also known as blanket weed, pond blanket weed, and a few, less desirable terms.

Pond Scum Control Advice


Filamentous algae, otherwise known as pond scum, is a nightmare for many pond and lake owners. The pond scum problem has a lot in common with other types of lake vegetation problems, and the cure for one will probably cure both. So, how do you get rid of pond scum? There are a number of different treatments, but the best method for dealing with pond scum is to prevent it from starting, and the method of prevention may come as a bit of a surprise.

Pond scum treatment

Pond scum, no matter where it ends up, starts at the bottom of the pond or lake. Pond scum is noticed most often on the surface of the lake or pond, but like emergent, or submersed lake weeds, it has its start on the lake bed. Pond scum treatments usually involve the use of a copper substance in liquid or granular form, or a contact weed killer like diquat. These products kill the algae, by punching tiny chemical holes in it, and the pond scum loses it's buoyancy and drops to the bottom. If you have this problem over a good portion of the lake or pond, it is best to treat only one third to one half of the lake at a time because the rotting vegetation requires oxygen to decompose, and it will take it from the water, which leaves less oxygen for your fish.

Pond scum removal

It is possible to physically remove pond scum from the surface of the water, but this process involves a good deal of manual labor in either skimming, or raking it. If you use copper sulfate or one of the other commercial herbicides labeled for pond scum or blanket weed control the algae will turn brown and sink to the bottom where it will degrade on it's own. Be aware that if you do not perform proper follow up procedures, the filamentous pond algae will return! Treatments of this type are sometimes needed, but such pond treatments are like the emergency room doctor after an auto accident. We are glad that he is there, but, it would have been better to have avoided the accident to begin with.

Preventing pond scum

Pond scum starts at the lake or pond bottom, it begins when sunlight penetrates to the bottom. Preventing light from reaching the bottom will prevent pond scum in the majority of cases. The prevention of pond scum, like the prevention of lake weeds requires doing something that will keep sunlight from reaching the lake bed. This involves water depth, and water clarity.

Adjusting water depth

There are two ways to change water depth. Raise the water level by adding water and maintaining it at a higher level, or removing soil from the bottom.

Raising the water level

Any attempt to raise the level of a spillway or overflow pipe should be preceded a thorough inspection  of the lake by someone who has the expertise to determine the success of such a project.

Removing soil from the lake bed

The other method for adjusting the depth of water in a pond or lake is to remove soil from the lake. This dredging process can be accomplished by draining the body of water and using earth moving equipment  to remove sediments, or by leaving the water, and hiring someone with specialized equipment built for the purpose. Either way, the project will be costly and time consuming. Ideally, there should be no area of the lake or pond that is less than 3 feet deep.

Adjusting water color

If water is too clear, then enough light can penetrate to produce filamentous algae. If sunlight can penetrate more than 24 inches, the water is too clear. There are colorants available which can do the job, but such colorants interfere with the natural food chain in the lake. The best means of producing color in a pond or lake is with tiny single cell algae known as plankton. Producing an "algae bloom" will reduce the depth to which sunlight can penetrate water, and prevent pond scum from becoming a problem. This is something that should be done even if your pond or lake is deep enough already. It will encourage the food chain and provide more healthy fish for your recreational fishing and for the table.

How to produce algae bloom

To start algae bloom, all that needs to be done is to add the proper amount of the proper fertilizer to the water. This should be done only after testing the water for proper pH, and amending the pH if needed. Once this is done, and the fertilizer added, the reaction will be swift. This should be followed by regular applications at 2 week intervals, and water clarity should be tested to be sure that it is working, and that water clarity is no more than 24 inches, and no less than 12 inches. If secchi depth is less than 10 to 12 inches, skip the next fertilizer application and re check the clarity periodically until it gets into the acceptable range before re starting the program.

Natural pond scum prevention with barley straw

There is evidence that pond scum can be prevented by using barley straw. The straw is submerged, or partially submerged in the water, and the decaying barley straw produces some chemical reaction that is not yet fully understood, but which seems to discourage filamentous algae production. It should be stated again, that this is not a treatment for existing pond scum, but another tool in our pond scum prevention kit. Remember that any algaecide, including barley straw is indiscriminate in pond algae destruction. When the pond scum is destroyed, there is a good chance that it will destroy the beneficial pond algae as well. Follow up is essential for for healthy ponds and lakes. For a paid consultation about dealing with your pond scum problem see:

Lake Consultation