Lake and Pond Treatment for Phosphorus Inactivation

Lake and Pond Treatment for Phosphorus Inactivation


The use of chemical precipitants to bind soluble reactive phosphorus (SRP) into an insoluble form that is unavailable to algae, and to clarify the water column.


To prevent eutrophication or rehabilitate those bodies of water considered eutrophic due to high concentrations of SRP.

Eutrophic pond with algal mats across the surface. Photo courtesy of Jim Ippolito.

How Does This Practice Work?

Aluminum sulfate (alum), polyaluminum chloride, ferric chloride or other on-the-market products (e.g., Clean-Flo International’s Bio Booster LQ; PET’s Phoslock) are individually dispensed in carefully controlled amounts to the affected water body. Aluminum, iron, or other chemicals react with the SRP to form complexes (e.g., aluminum or iron phosphate minerals) that are insoluble at pH values of most waters.

In the case of aluminum or iron-based products, the aluminum or iron undergoes hydrolysis to form an aluminum (or iron) hydroxide that clarifies the water column by creating a floc that binds to sediment suspended in the water column. Aluminum (or iron) hydroxide also has the ability to strongly sorb and remove SRP from the water column.

Sediment in return flow irrigation water. Photo courtesy of Jim Ippolito.

The aluminum(or iron) hydroxide-SRP solids and flocculated sediment particles settle to the bottom of the lake or pond. The reaction between aluminum (or iron) hydroxide and phosphorus is practically irreversible.

Where This Practice Applies and Its Limitations

Chemical treatment of lakes, ponds and reservoirs is a relatively common practice, as long as the water body to be treated is not excessively large (e.g., Lake Erie). The first US lake treated occurred in 1970, and hundreds have been treated since.

The application can be a single dose determined to inactivate the water column SRP or to prevent phosphorus (P) recycling from deposited bottom sediments. In several states, alum or polyaluminum chloride are injected proportional to storm flow for (sub)urban stormwater, and edge-of-field or return flow runoff in and from agricultural sites.

Alum or polyaluminum chloride injections to control soluble reactive P. Photo courtesy of Jim Ippolito.

Larger water bodies are typically treated with liquid alum, polyaluminum chloride, ferric chloride, or other on-the-market chemicals. Applications typically are carried out by experienced applicators and/or limnologists. Smaller lakes and ponds can be treated with dry alum.

It is important to note that alum, polyaluminum chloride, and ferric chloride can lower water pH. An established practice is to maintain the water pH between 6 and 7.5 during treatment. If the receiving water is already low in pH or low in alkalinity, buffered alum will be better at maintaining water pH. Other alkalis like sodium aluminate at two gallons of alum + one gallon of sodium aluminate are effective in treating P without adversely impacting pH. It is important to note that drastically decreasing water pH can adversely affect aquatic life.

Thus, checking with the manufacturers or a qualified water treatment specialist before treating lakes, ponds or reservoirs is a must. A critical component of the success of this practice is accurate and complete water quality determinations for pH, alkalinity, total P and SRP. The pond or lake size and volume must be accurately determined in order to calculate a chemical application rate. Influent water quality, volume, and sediment characterizations are also important to discern in order to ensure accurate chemical dosage.


Lake and pond nutrient inactivation treatment will reduce algal numbers and clarify water. For severely polluted waters, an algaecide may be needed to kill the algae and move P in  dead algal bodies to the bottom of the water column where chemical treatment can help inactivate the SRP.

If further inputs of P to the lake or pond are managed, nutrient inactivation can last 10 to 20 years. Lakes with uncontrolled nutrient inputs may need routine re-treatment or on-demand, automatic chemical injection application systems. In addition to chemical controls of in-lake/pond P, attempts to decrease P inputs into water bodies should further reduce P within the waterbody.

Cost of Implementing the Practice

The cost of a P inactivation program will depend on:

  • size/volume of the water body;
  • degree of P pollution;
  • water chemistry;
  • actual chemical costs, including shipping;
  • chemical effectiveness for removing P from the water column;
  • if buffering chemicals are needed to maintain water pH;
  • if on-demand chemical feed control application systems are used;
  • site access, and if land is required to install on-site housing for chemicals and/or electronic dispensing equipment;
  • if application contractors are used; and
  • consulting fees.

From simple to more complex applications, costs for chemicals and application may vary from a few hundred dollars per acre to thousands of dollars per acre of surface water.

Operation and Maintenance

Maintenance of P inactivation programs is mostly focused on water quality monitoring to make sure additional SRP inputs are controlled. Periodic tests for pH, alkalinity, total P and SRP, chlorophyll a and turbidity/transparency will aid in the assessment of effectiveness and longevity of treatment.

On-demand systems will require preventative maintenance of the dosing and control systems. Pumps utilized for this type of application are often similar to those used in disinfectant applications in dairy systems or medication pumps (e.g., peristaltic pumps) used in the animal industry. Yet, they could be made to be simpler via human controlled valves. Or, they could be made complex to inject a proper chemical dose at a proper time via the use of electronics such as Arduino controllers. Eventually, these complex chemical injection systems likely could interface with in-water sensors that quantify water chemistry characteristics in real-time.


Charboneau, D. 1999. Chemical precipitation and inactivation as a method to reduce internal phosphorus loading in lakes.

Hargreaves, J.A. 1999. Control of Clay Turbidity in Ponds. Southern Regional Aquaculture Center Publication No. 460.

Harper, H.H. no date. Current research and trends in alum treatment of stormwater runoff.

Helfrich, L.A., and T. Newcomb, 2009. Clearing Muddy Pond Waters. Virginia Cooperative Extension Publication 420-250.

Ippolito, J., and D. Bjorneberg. The use of wetlands and chemical injections to control sediment and soluble phosphorus.

Minnesota Pollution Control Agency. 2022. Lake protection and management.

Neethling, J.B. 2013. Optimizing chemical phosphorus removal.

North American Lake Management Society. 2004. The use of alum for lake management.

North American Lake Management Society. 2017. Lake management success stories.

Pilgrim, K.M., and P.L. Brezonik. 2005. Treatment of lake inflows with alum for phosphorus removal.

Reddy, G.B., D.A. Forbes, P.G. Hunt, and J.S. Cyrus. 2011. Effect of polyaluminum chloride on phosphorus removal in constructed wetlands treated with swine wastewater. Water Science Technology. 63(12):2938-2943.

Wagner, T., and L.E., Erickson. 2017. Sustainable management of eutrophic lakes and reservoirs.

Wisconsin Department of Natural Resources. 2003. Alum treatments to control phosphorus in lakes.

For Further Information

Contact your local soil and water conservation district, USDA-NRCS or Cooperative Extension Service office. To find your local USDA Service Center, visit

Additional information may be obtained from the North American Lake Management Society at and local water-treatment chemical manufacturers.

Current Author
Jim Ippolito
Colorado State University
Previous Author
Christopher Lind
formerly of General Chemical Company
Editing and Design
Deanna Osmond
NC State University
Forbes Walker
University of Tennessee

Ipollito, J. 2023. Lake and Pond Treatment for Phosphorus Inactivation. SERA17 Phosphorus Conservation Practices Fact Sheets.

Funding for layout provided by USDA-NRCS Grant 69-3A75-17-45
Published: Feb 25, 2023