Algae Control Methods

Sodium Carbonate Peroxyhydrate | Endothall | Diquat | Grass Carp | Raking | Shading Products | Microbial Products | Barley Straw | Phosphorus Inactivation | Permits

Algae control options

The amount of algae in a lake depends on the amount of nutrients available for growth (mostly phosphorus). Long-term management of algae involves nutrient reduction to the water body. However, long-term nutrient reduction can be costly and take many years for significant improvement in water quality. There are some short-term algae control treatment options and some "home remedies" available for managing algae problems in the meantime. Most of the methods presented on this page are short-term.  Phosphorus inactivation may result in longer-term control of algae than other methods discussed here. There is a state-wide effort to reduce phosphorus on household products like detergents. Click here to read about reducing phosphorus pollution to improve water quality.

Sodium carbonate peroxyhydrate products

These Environmental Protection Agency (EPA)-registered sodium carbonate peroxyhydrate products are fast acting algaecides (algae killer) or algaestats. Algaestats do not kill algae outright but instead inhibit their growth, preventing bloom formation. Lake managers apply these products to the water to prevent algal blooms or to treat existing algae. Lake managers use these products as an alternative to copper-based algaecides not allowed in most Washington water bodies. In some parts of the world, there are copper-resistant algae strains and these products provide an alternative to treat copper-resistant algae.

The EPA registered sodium carbonate peroxyhydrate products for use in ponds, lakes, reservoirs, and drinking water sources. Sodium carbonate peroxyhydrate acts as an oxidizing agent to kill algae. When applied to water, these granular products break down into sodium carbonate and hydrogen peroxide. Some anecdotal evidence suggests that sodium carbonate products are more effective when used to prevent the occurrence of algae blooms. Waiting until the water turns green may not be the best time to treat. Some people claim that these products successfully spot-treat filamentous algae. Several brands of sodium carbonate peroxyhydrate products are on the market including GreenClean™ and Pak 27™. Some brands are advertised as being selective to blue-green algae.

Endothall- amine salt (e.g., Hydrothol 191™) products

Hydrothol 191™ (with an active ingredient of endothall-amine salt) is a rapidly-acting, non-selective, contact herbicide or algaecide. In Washington, Hydrothol 191™ may only be used at very low concentrations for filamentous algae or blue-green algae control. Lake managers may need to treat several times each season to control algae. Hydrothol 191™ has a high acute toxicity to fish. Because of potential fish impacts, Ecology does not allow concentrations higher than 0.2mg acid equivalent per liter of Hydrothol 191™  in Washington waters. There is also recreational restrictions for 24 hours after treatment in Washington. There is some evidence that at these low concentrations, Hydrothol 191™  acts as an algaestat rather than an algaecide. Hydrothol 191™ does not accumulate in sediments and breaks down rapidly. (Click here to read Ecology’s risk assessment for endothall products)


Diquat is an EPA-labeled rapidly-acting, non-selective, contact herbicide that is applied as a liquid. Muddy water or water with lots of organic material can interfere with its effectiveness. Diquat is normally applied to control the growth of nuisance aquatic plants. Although the label for diquat does not claim any efficacy in treating algae, applicators have reported that diquat does appear to kill or suppress the growth of some species of algae. (Click here to read Ecology's risk assessment for diquat)

Grass Carp

Grass carp, a fish species native to Asia, feed on aquatic plants and filamentous algae. Grass carp are biological tools used to control nuisance growth. Grass carp stocked into Washington lakes must be certified disease free and sterile. Fish farmers create sterile fish (called triploids because they have an extra set of chromosomes) by subjecting fish eggs to temperature or pressure shock. Testing verifies that grass carp are sterile. In Washington, lake managers use grass carp to control the excessive growth of aquatic plants. Grass carp exhibit definite food preferences and consume some aquatic plant species more readily than others. Grass carp may control filamentous algae, although filamentous algae is not a preferred food. Grass carp may eat aquatic plants before eating filamentous algae. Some reports indicate that adding grass carp to a lake may promote the growth of other algae. Learn more about grass carp.


Lake residents can remove filamentous algae from the water using a sturdy rake with a rope attached to the end. The operator throws the rake into the water and pulls the rake and filamentous algae to shore. Compost the algae and use it in the garden. Raking is effective for small areas of filamentous algae but is time consuming and labor intensive when controlling larger areas. In addition, filamentous algae grows back quickly and may move around the water body through wind and wave action. Sometimes raking becomes a never-ending chore during summer months. Also, raking cannot remove blue-green algae and many other types of algae.

Shading products (aquatic dyes)

Shading products, formulated and EPA-registered for aquatic use, do not kill algae or submerged plants directly but limit their growth by reducing the amount of sunlight that reaches them. The United States Food and Drug Administration approved the dyes used in these shading products for food, drug, and cosmetic color additives.

For effective use, apply shading products early in the growing season before plants and algae have started growing. Shading products perform best in water bodies greater than two feet in depth. Adding these products to the water once algae blooms or filamentous algae mats are floating on the water or after aquatic plants are within two feet of the waters surface is less effective. Maintain the dye concentration throughout the growing season for good control of algae and submerged aquatic plants. You may need to add more product every month to maintain the color, or more frequently in areas with high rainfall.

Apply shading products to small water bodies such as some golf course or backyard ponds that do not discharge to surface waters of Washington State (streams and rivers). Shading products change the water color to blue, turquoise, or blue-green. Some people find this color pleasing while others may not. When the color fades, add more product to the water to maintain shading properties.

EPA has not registered all shading products and these products are not approved through the EPA-registration process. By law, sellers of unregistered products may not claim that they affect algal growth.

See also the EPA re-registration document for one brand of a shading product called Aquashade™ at: 

Microbial products

Microbial products are live bacterial products. When added to ponds and lakes, companies selling these products allege that they reduce organic material on the lake bottom. Companies do not advertise these microbial additives as algaecides and EPA has not registered these products as algaecides. However, their manufacturers claim that their use leads to less algal growth in ponds and small water bodies. Little information exists in the scientific literature about their effectiveness in reducing algal growth. Two peer-reviewed studies on several commercial bacterial products showed no control of algae. In anecdotal reports, some users believe that their ponds have less muck and produce less algae with microbial product use. Washington only allows the use of microbial products in water bodies with no discharge to surface waters of the state during and for two weeks after treatment.

Barley straw

Using barley straw or any other straw for algae control is considered to be a "home remedy." EPA has not registered barley straw as an algaecide or algaestat. This excellent article from Purdue University sums up the status of barley straw use in the United States. It also provides information about how to use barley straw in ponds and other water bodies.

Phosphorus inactivation products (aluminum sulfate, sodium aluminate, and calcium hydroxide/carbon dioxide)

Phosphorus generally limits the growth of freshwater algae in most Washington lakes. A direct relationship exists between the amount of phosphorus in a lake and the amount of algae growing in the lake. As phosphorus levels increase, the amount of algae increases too. At very high levels of phosphorus, other nutrients or light may limit the growth of algae. Long-term management of excessive algae requires the removal of phosphorus sources to the water body. Reducing phosphorus inputs removes a key algal nutrient.

External sources of phosphorus such as stormwater runoff, septic system effluents, fertilizers, pet wastes, waterfowl, agriculture, and even rainfall can contribute phosphorus to a lake. Remove or modify as many of these phosphorus sources as possible. Sometimes even removing external sources is not enough. Phosphorus-enriched sediments can release phosphorus to the water through a process known as internal loading. When sediments are contributing phosphorus to the lake, lake managers can use nutrient inactivation techniques to remove phosphorus from the water column (called precipitation) and to retard its release from the sediments (called inactivation).

Lake managers use aluminum, iron, or calcium salts for phosphorus inactivation of lake sediments. Aluminum sulfate (alum) is the most commonly used nutrient inactivation chemical for lake projects. Managers may also apply alum in small doses to precipitate water column phosphorus. When applied to water, alum forms a fluffy aluminum hydroxide precipitate called a floc. As the floc settles, it removes phosphorus and particulates (including algae) from the water column (precipitation). The floc settles on the sediment where it forms a layer that acts as barrier to phosphorus. As sediments release phosphorus, it combines with the alum and is not released into the water to fuel algae blooms (inactivation). Algal levels decline after alum treatment because alum addition reduces phosphorus levels in the water.

Nutrient inactivation is only appropriate where internal loading is a significant phosphorus source. If most phosphorus comes through external sources, alum treatment will not be effective. For appropriate nutrient inactivation projects, the length of treatment effectiveness varies with the amount of alum applied and the depth of the lake. Alum treatment in shallow lakes for phosphorus inactivation may last for eight or more years. In deeper lakes, alum treatment may last far longer.

For a scientific explanation of phosphorus inactivation chemistry and techniques please see: the third edition of Restoration and Management of Lakes and Reservoirs, edited by G. Dennis Cooke, 1995.

For more information about alum treatment see:

Permits needed

In Washington, EPA-registered aquatic products must be applied by a licensed applicator. Permits may be required for the application of herbicides, algaecides, shading products, microbial products, and barley straw. See the Aquatic Plant and Algae Management permit to determine whether this permit is needed for your project. It is also important to check with your local jurisdiction before proceeding with any treatment. Sometimes local governments have additional environmental permitting requirements.

Grass Carp - For Washington residents, a private fish stocking permit must be obtained from the Washington Department of Fish and Wildlife. Also, if inlets or outlets need to be screened, an Hydraulic Project Approval application must be completed for the screening project.

Raking - The Washington State Department of Fish and Wildlife requires a permit called an Hydraulic Project Approval for all activities taking place in the water, including raking.

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