Phosphorus Pollution

Phosphorus is a chemical element found naturally in many types of minerals. It is widely used in artificial fertilizers, and is present in large amounts in organic waste like manure.

When too much phosphorus gets into our lakes, rivers and waters, it overloads them with too many nutrients. In Wisconsin, the main causes of phosphorus pollution are “nonpoint sources” like agricultural fields, where rain or melting snow carries phosphorus-rich waste into waterways. The excess nutrients cause plant and bacterial overgrowth, including potentially toxic algae blooms.

In 2010, Wisconsin passed a set of rules to reduce phosphorus pollution and preserve water quality. These rules set limits for how much phosphorus could be in water bodies, and established new strategies (like the “Adaptive Management Option”) to keep phosphorus levels below those limits.

Key Points

  • Phosphorus pollution is one of the largest causes of water quality problems in Wisconsin.
  • Of the more than 700 water bodies listed as “impaired” in Wisconsin, one-quarter fail to meet water quality standards due to phosphorus pollution.[1]
  • Phosphorus pollution can cause algae blooms that decrease the usability of waters and threaten the health of people and the environment.
  • Runoff is the main source of phosphorus pollution in Wisconsin, but working together through the AMO, farmers and municipalities can significantly reduce phosphorus pollution and improve the quality of our waters.
Clean Wisconsin's Work

The excess phosphorus from agricultural runoff and other sources is a major pollution threat to Wisconsin’s waterways. It causes overgrowth of aquatic plants and bacteria, including the harmful cyanobacteria (blue-green algae) blooms capable of producing toxins dangerous to humans, especially children.

Clean Wisconsin has been fighting for clean water since we supported the EPA and DNR water quality standards in 1987, and we support laws to reduce phosphorus accumulation in our lakes, rivers and streams. We hope to rid our waters of algae blooms to make waters in Wisconsin clean, safe and enjoyable.

In 1992, we established rules creating point source discharge limits for phosphorus and Wisconsin’s Nonpoint Pollution Act. In 2009, we helped pass rules that restrict the use of lawn fertilizers and automatic dishwashing soap containing phosphorus. In 2010, we were instrumental in passing the innovative new phosphorus rules that establish numeric standards for phosphorus in our waters and allow for creative strategies for meeting these standards. Clean Wisconsin continues to support these laws.[2]

Clean Wisconsin Media and Materials


Questions and Answers

What is phosphorus?

Phosphorus is a chemical element that is found naturally in air, rocks, soil and organic materials. It is essential for life, and one of the main chemicals necessary for plant growth. As a result, the biggest use of phosphorus is in artificial fertilizers. Phosphorus is also present in large amounts in fecal matter from both humans and animals, as well as being in some household products.

When too much phosphorus enters our lakes, rivers and other waters, it can overload them with nutrients. This can damage the ecosystems that exist in those waters, and lead to problems like eutrophication and algal blooms.

What is eutrophication?

Eutrophication is the process of biological material (also called biomass) building up in bodies of water over time. This process can lead to changes in the ecosystem and aquatic life that the water supports. Eutrophication occurs when a body of water receives extra nutrients, stimulating additional plant growth. Though eutrophication can occur naturally, it can also be artificially quickened by human activities that contribute phosphorus and other nutrients to water bodies. Phosphorus pollution is the primary driver of eutrophication in Wisconsin.

Why is eutrophication bad?

Eutrophication has a negative impact on our health, our tourism, and water recreation like fishing and boating. Human additions of phosphorus to aquatic ecosystems cause eutrophication at a level much higher than would naturally occur. This reduces water quality, which can have many impacts – for example limiting the types and number of fish that can thrive in the water.

One of the main problems with eutrophication is when aquatic algae blooms in the water. These blooms can crowd out other aquatic life by covering the water and blocking sunlight, making it impossible for organisms deeper in the water to grow. As a result, the blooms reduce overall plant growth, which lowers the amount of oxygen at certain depths in lakes, and can kill many fish and other wildlife. This can throw the entire ecosystem off balance. The algae blooms are also foul-smelling, unsightly and can become toxic. The toxins from algae blooms can accumulate in fish tissues and make them unsafe to eat. Especially bad toxic algae blooms have made people sick and killed animals. For more information, see the Blue-Green Algae page.

What can be done to reduce algae blooms? 

The easiest and best way to combat algae blooms is to prevent the phosphorus that feeds them from getting into the water in the first place. This can be achieved by reducing phosphorus use or by managing phosphorus-containing waste, particularly manure, more effectively. For more information, see the Blue-Green Algae page.

How does phosphorus get into Wisconsin’s waters?

In Wisconsin, the largest sources of phosphorus pollution are so-called “nonpoint sources.” These are sources like agricultural fields, where rain or melting snow carries phosphorus-rich waste into waterways. They are called “nonpoint” because the pollution doesn’t necessarily all come from a single location – like the outlet pipe of an manufacturing plant.

Other “point” sources of pollution that also contribute significant amounts of phosphorus to our waters include municipal wastewater treatment plants and industrial facilities. The specific point of discharge from these types of sources makes them generally easier to monitor and control, which is why they have historically been more regulated than nonpoint sources. In Wisconsin though, the new phosphorus rules include a unique strategy, called the Adaptive Management Option (AMO), that has the potential to be a more flexible and cost-effective strategy than traditional cleanup options because it focuses on collaboratively reducing all sources of phosphorus, particularly runoff, across a watershed.

What are Wisconsin’s Phosphorus Rules?

Wisconsin’s Phosphorus Rules are in the Wisconsin Administrative Code chapters NR 102, NR 151 and NR 217. These rules create new standards for the amount of phosphorus in our waters, including limits on phosphorus coming from both point sources, like sewage treatment plants, and nonpoint sources, like agricultural fields. The rules also established the Adaptive Management Option for phosphorus, explained below.

What is the Adaptive Management Option for phosphorus?

The Adaptive Management Option (AMO) is a new regulatory phosphorus pollution reduction strategy in Wisconsin. It was created to be one of several options available to facilities for achieving Wisconsin’s phosphorus water quality standards. By using AMO instead of installing expensive new phosphorus control technologies at a particular facility, facilities can clean up rivers and lakes by working with other sources of phosphorus in the area, particularly upstream sources of runoff. This option gives those facilities the flexibility to pursue the most efficient management options to achieve clean water. By working at a watershed level, the AMO also creates an opportunity to achieve extra water quality benefits.

Quick Facts
  • Polluted runoff is one of the biggest threats to Wisconsin’s waters.[1]
  • As much as 80% of phosphorus pollution in Wisconsin can be attributed to nonpoint sources, usually agricultural.[1]
  • Phosphorus promotes excess plant growth and makes toxic algae blooms more likely.
  •  Each pound of phosphorus entering the water can produce 300 pounds to 500 pounds of algae.[4]
  • Over the past 3 years, 98 people have reported health complaints related to such blooms resulting from excess phosphorus in waterways.[1]
Wisconsin Data, Trends, and Legislation

Wisconsin has 172 waterways that are impaired primarily due to phosphorus.[3] Phosphorus entering our waters has greatly increased eutrophication and the growth of algae blooms in the state.[1] In response, Wisconsin has taken initiative to pass laws to reduce the amount of phosphorus entering our lakes and rivers. In 2009, a bill to restrict phosphorus in cleaning products passed, marking the beginning of more stringent phosphorus regulation in Wisconsin. In 2010, the Phosphorus Rules revision package passed. This included changes to the state Administrative Code that were designed cooperatively to decrease the amount of phosphorus in our waters by targeting multiple different sources of phosphorus pollution.

Current Law

There are several Wisconsin rules that relate to phosphorus control. The set of phosphorus control rules passed in 2010 appears in the following chapters of the Wisconsin Administrative Code:

  • NR 102 sets numeric standards for the levels of phosphorus that may be allowed in Wisconsin’s water bodies without degrading water quality.
  • NR 151 outlines procedures for managing polluted runoff and restricts agricultural practices that can contribute to runoff.
  • NR 217 establishes procedures for setting discharge limits for phosphorus and strategies that permitted dischargers can use to meet these limits, including the Adaptive Management option.

Additionally, Assembly Bill 281, placed in Wisconsin statute in 2009, lowers the amount of phosphorus allowed in automatic household dishwashing soaps from 8.7% by mass to 0.5% by mass.  Other changes, such as a ban on phosphorus in lawn fertilizer and tightening of rules for concentrated animal feeding operations (CAFOs), have also occurred in the last few years.


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Please cite this resource as: Clean Wisconsin, Inc. “Phosphorus Pollution.” Clean Wisconsin Enviropedia. Retrieved from