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Additional Protections For Some Colorado Waters: Antidegradation

                                                                                                                                                      en español



All state waters in Colorado are protected for their classified uses: drinking water supply, aquatic life, recreation and/or agriculture. 

All waters in Colorado are protected for water quality. There are additional Antidegradation protections for some waters to prevent those waters from getting significantly worse. 




The uses of the water (drinking water, aquatic life, recreation, and agriculture) are protected. 


Some antidegradation protections. Requires an extra level of review to maintain water quality. No significant degradation is allowed.


Provides the greatest amount of antidegradation protection and existing quality must be maintained. Strict antidegradation protections. No permanent degradation is allowed (e.g. in national parks).

*Under any tier, the state works to ensure that uses are protected no matter what and that dischargers are not permitted to cause or contribute to a violation of water quality standards.


WHAT ARE SOME EXAMPLES OF WATERS WITH ANTIDEGRADATION PROTECTIONS? These can be “reviewable” or “outstanding” waters.

  • The South Platte Segment 14 (South Platte River through downtown Denver) is designated a “reviewable” water. 
  • Many waters in Rocky Mountain National Park are designated as “outstanding” waters. 


  • Examples:
    • The Lower Arkansas Segment 1a (The Arkansas RIver from Fountain Creek to near Avondale, which is east of Pueblo) is a “use-protected” water.  
    • The Upper South Platte Segment 15 (The South Platte River from the Burlington Ditch diversion in North Denver to the Big Dry Creek confluence near Fort Lupton) is a “use-protected” water.  




  • Through public rulemakings for regulations - anyone can participate.  Antidegradation protections are based upon recommendations from stakeholders and the state using the best available data and science. To learn more, go to


Current Antidegradation Regulations:

Recent Updates to the Antidegradation Rule:

Current Antidegradation Rulemakings (Potential Changes to Current Regulations):

  • A rulemaking hearing is currently scheduled for September 2022 to consider antidegradation designations for three segments in the South Platte Basin. The three segments under consideration are for portions of Clear Creek (between Youngfield Street in Wheat Ridge to the confluence with the South Platte River), and the Upper South Platte (from Burlington Ditch in Denver to the confluence with Big Dry Creek) and Middle South Platte River (from Big Dry Creek to the confluence with St. Vrain Creek). 
    • More information can be found at: Regulation #38, Classifications and Numeric Standards for South Platte River Basin, Laramie River Basin, Republican River Basin, Smoky Hill River Basin
    • Participation in the hearing is encouraged at the hearing. More information can be found in the Public Participation Handbook. The Notice of Public Rulemaking Hearing includes key information, dates and deadlines. 
      • Schedule of Important Dates
        • Proponent’s prehearing statement due 6/1/2022 at 5:00 pm
        • Party status requests due 6/15/2022 at 5:00 pm
        • Responsive prehearing statements due 7/6/2022 at 5:00 pm
        • Rebuttal statements due 8/3/2022 at 5:00 pm
        • Prehearing Conference 8/15/2022 at 1:00 pm


Permits are where antidegradation protections become legally enforceable for specific dischargers. For more information about permits, see this slideshow.


  • The Water Quality Control Division, which is part of the Colorado Department of Public Health and the Environment, issues permits under the Clean Water Act and the Colorado Water Quality Control Act. 
  • We welcome and encourage public involvement in permits! Before any individual or general permit is issued, the Water Quality Control Division will publish a draft permit for public comment on its public notice website. The division will consider all comments before taking further action and respond to all comments in the final permit. 


  • Colorado has a detailed guidance document about how it implements antidegradation in permits. This is the best source of information if you have specific questions.
  • Any permit issued by the Water Quality Control Division for reviewable waters must prevent significant degradation of those waters since the date when the stream first became reviewable. We call this the baseline date.
  • Significant degradation can mean a permanent increase in pollution of 15% since the baseline date - but even a smaller increase in pollution can be significant. It depends upon what kind of pollutant it is, the conditions of the stream, other nearby dischargers and how much they are polluting, etc. 
    • Colorado’s Antidegradation Guidance includes more information about how to determine when the degradation is significant. This is the best source of information if you have specific questions.
    • On the flip side, if the facility discharges to a really large stream or river (so that there is a lot of dilution), there may not be significant degradation even if it is a big increase.

Permits In Practice:

  • Facilities that started discharging after the baseline date (new dischargers) are required to get fairly low antidegradation limits in order to prevent significant degradation. For instance, in some permits, the antidegradation limit for new permittees is 15% or less of their regular pollutant limits.
  • Temporary dischargers (less than 2 years) are excluded from antidegradation requirements.
  • Facilities with small waste streams that discharge to large streams or rivers (so they have 100:1 dilution) are excluded from antidegradation requirements.
  • Existing dischargers usually do not get especially low antidegradation pollution limits (like new dischargers). Instead, existing dischargers may be allowed to continue discharging the same amount of pollution as they were when the stream became reviewable (the baseline date). These antidegradation limits are something called “NILs” (Non-Impact Limits) and “Implicit NILs.”
    • NILs are discussed on page 6 of the Antidegradation Guidance
    • Here is a plain language description of NILs.
    • Even with NILs, if a discharger increases their flow, their limits will get stricter.
    • The division is developed a memo to better clarify how implicit NILs are determined. Clarifications of Antidegradation Guidance Regarding Implementation of Implicit Non-Impact Limits (NILs), can be found here.

The Exception To Antidegradation Protections - Antidegradation Alternative Limits:

  • The Water Quality Control Division can determine that allowing more degraded water quality is necessary to accommodate important economic or social development and give a discharger a more lenient “alternative” antidegradation limit.
    • See Regulation 31.8(3)(d) (referring to this as the “Necessity of Degradation Determination”).
    • This is also called an “Antidegradation Alternative Analysis.” 
  • The division is currently developed guidance for submitting an application for an alternative antidegradation limit.
    • The workgroup materials, including examples, can be found here.
    • Click this link for the draft guidance.
  • All antidegradation alternative limits must meet the requirements in Regulation 31.8(3)(d) and are subject to a public comment process. 


  • If a stream does not have antidegradation protections, can dischargers obtain permits that would violate stream standards?
    • No. Streams or other waters that do not have antidegradation protections still have water quality standards to protect existing uses and other classified uses. Any permit authorizing pollution to those streams must ensure that those stream standards are not violated and those uses are protected. 
  • How may I participate in upcoming Water Quality Control Commission rulemaking hearings?
    • Participation in Water Quality Control Commission rulemaking hearings is encouraged. Interested persons may participate formally in the rulemaking process by obtaining party status or participation can be as a member of the public providing comments. Persons with party status must meet certain prehearing deadlines for the submission of documents. For more information on public participation, visit the commission’s website.
  • Where can I find final decision documents by the Water Quality Control Commission?
  • Who may I contact to learn more? 


  • Baseline - The water quality on the the date that the Water Quality Control Commission gave a waterbody antidegradation protections (like making a stream reviewable)
  • Commission - Water Quality Control Commission. The administrative agency responsible for developing specific water quality policy in Colorado, in a manner that implements the broader policies set forth by the Legislature in the Colorado Water Quality Control Act. The commission adopts water quality classifications and standards for waters of the state, as well as various regulations aimed at achieving compliance with those classifications and standards. The Colorado Water Quality Control Commission meets the second Monday (and Tuesday, if necessary) of each month.
  • Dischargers - Anyone who puts pollutants into a state water with a state permit
  • Division - Water Quality Control Division. The Water Quality Control Division monitors and reports on the quality of state waters to prevent water pollution, protect, restore and enhance the quality of surface and groundwater while ensuring that all drinking water systems provide safe drinking water. The division inspects water systems, issues permits, ensures compliance, and takes action against entities who violate state and federal regulations. The division works in partnership with utilities, counties, and other agencies to oversee, improve, and maintain quality drinking, surface, and ground water.