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Wisconsin's Phosphorus Rule


Phosphorus has long been recognized as the controlling factor in plant and algae growth in Wisconsin lakes and streams. Small increases in phosphorus can fuel substantial increases in aquatic plant and algae growth, which in turn can reduce recreational use, property values, and public health.

Sources of excess phosphorus

Phosphorus entering our lakes and streams comes from "point sources" — piped wastes such as municipal and industrial wastewater treatment plants that release liquid effluent to lakes and rivers or spread sludge on fields; and from natural sources, including past phosphorus loads that build up in lake bottom sediments.

Phosphorus also comes from "nonpoint" or "runoff" pollution. Such pollution occurs when heavy rains and melting snow wash over farm fields and feedlots and carry fertilizer, manure and soil into lakes and streams, or carry phosphorus-containing contaminants from urban streets and parking lots.

Protecting human health and welfare

To protect human health and welfare, revisions to Wisconsin's Phosphorus Water Quality Standards for surface waters were adopted on Dec. 1, 2010. These revisions were as follows.

  • Created water quality standards for phosphorus in surface waters. These standards set maximum thresholds for phosphorus in Wisconsin’s surface waters. See Chapter NR 102 [exit DNR].
  • Set procedures to implement these phosphorus standards in WPDES permits issued to point sources discharging to surface waters of the state. See Chapter NR 217 [exit DNR].
  • Helped to curb nonpoint sources of excess phosphorus by tightening agricultural performance standards. See Chapter NR 151 [exit DNR].


Any permit reissued after December 2010 will be evaluated for phosphorus water quality-based effluent limits. Some phosphorus limits may be restrictive, while others can be easily met. Department staff has developed supporting resources to assist in phosphorus rule implementation including Guidance for implementation of Wisconsin’s phosphorus water quality standards [PDF]. Please note that this document may be evolved as the department addresses more of the many unique circumstances related to phosphorus implementation.


Many facilities will be required to optimize their wastewater treatment plant to increase the removal of total phosphorus. This optimization is part of a comprehensive program to achieve water quality standard based limits for phosphorus. The department has developed a phosphorus operational evaluation and optimization report worksheet [PDF] to aid in this effort.

Compliance options

Contact Matt Claucherty for more information about economic variances.

  • Facility upgrades: Facilities can choose to add treatment technology to their plant to comply with the new phosphorus limits. This is the traditional method used to comply with permit limits.
  • Water quality trading: Water quality trading allows point sources to offset their pollution load and comply with phosphorus limits by taking credit of other phosphorus reductions within the watershed.
  • Adaptive management: Similar to water quality trading, adaptive management allows a point source to reduce other sources of phosphorus pollution within a watershed to achieve compliance with phosphorus requirements. Unlike water quality trading, however, adaptive management focuses on improving water quality, rather than simply offsetting a permit limit
  • Economic hardship variances: In some cases, the available compliance options are simply too costly and would result in an economic hardship for the community or industry. In these cases, the discharge can request an economic variance. Variances allow communities to take economically viable steps towards compliance. Forms are available to help streamline the variance request process.

Options to adjust restrictive phosphorus limits

  • TMDL-derived limits: Total maximum daily loads (TMDLs) create a balanced approach to address point and nonpoint source of phosphorus pollution in watersheds currently impaired by excess phosphorus. Given this, point sources in TMDL watersheds tend to receive less stringent permit limits. To address excess phosphorus,
  • Site-specific criteria: Site-specific phosphorus criteria can provide facilities with less stringent phosphorus limits in cases where water quality goals are being attained, despite their being elevated phosphorus levels in the receiving water.