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​Regulatory environment

   This study is not an investigation of regulatory compliance. It is, instead, an examination of trout habitat health, using comparisons with water temperature and water quality criteria and standards that are relevant in the basin.

  I. Water temperature​​​

    Background | Regulatory 

Temperature logger in protective case

     A. Stream classification

  1. The main stem and tributaries in the study area are Colorado Cold Stream Tier 1 (CS-1) waters [1, 2].

  2. Water use classifications are Agriculture, Aquatic Life Cold 1, Recreation E, and Water Supply [1].

  3. Agriculture means "suitable for irrigation of crops" and not hazardous as livestock drinking water [3].

  4. Aquatic Life Cold 1 can sustain a "wide variety of cold water biota, including sensitive species" [3].

  5. Recreation E is "used for primary contact recreation" [3].

  6. Water Supply is "suitable...for potable water supplies" [3].

  7. Colorado's table value standard (TVS) for chronic and acute water temperatures are 62.6 and 71.1 F [1].

  8. They are aquatic life class 1 and apply for the period of June-September [1].

  9. Colorado requires "no increase in temperature...deemed deleterious to the resident aquatic life" [1].

  10. Cutthroat and brook trout are the "species expected to be present" at the CS-1 streams [1].

  11. The chronic criterion is for protection from sublethal warm temperatures [3-5].

  12. That is, temperatures that can diminish long-term growth, reproduction, and survival [3-5].

  13. The acute criterion is for protection from lethal exposures to very warm temperatures [3-5].

    B. Application of criteria

  1. The weekly average temperature (WAT) is evaluated against the chronic criterion.

  2. WAT is the "average of daily average temperatures over a seven-day consecutive period" [3, 4].

  3. The two-hour average temperatures (TAT) is evaluated against the CO acute criterion.

  4. TAT is the "highest two-hour average water temperatures...during a given 24-hour period" [3, 4].

  5. The maximum TAT, or MTAT, is the largest of rolling two-hour averages.

  6. MTAT and daily maximum temperature, DM, are the same.

  7. The study compares measured water temperatures with the CO chronic and acute criteria [1].

  8. Those values were set for protection of Colorado's native species, cutthroat trout, in particular [5}.

  9. This study also compares temperature for other basin-resident trout species, that is, wild trout.

  10. The chronic criteria used are: rainbow, 64.6 F; brook, 64.9 F; and brown, 67.3 F [5].

  II. Water quality​​

Test 1
Sampling for water quality analysis
Roaring Forks.JPG
  1. This study uses:

  • E. coli: 126 per 100 ml

  • Nitrate: 10 mg/l

  • Ammonia: calculated based on pH

  • Metals (cadmium, copper, lead, manganese, silver, zinc): calculated based on hardness

  • Selenium: 4.6 ug/l

2. This study also uses the aquatic life class 1 standard for arsenic, which is calculated based on hardness.

3. Colorado defines "existing quality” as the:

  • 85th percentile of the data for ammonia, nitrate, and dissolved metals

  • 50th percentile for total recoverable metals

  • 15th percentile for dissolved oxygen

  • Geometric mean for E. coli

  • Range between the 15th and 85th percentiles for pH

4. In addition, the study applies these Colorado interim standards for nutrients:

  • Total nitrogen as nitrate: 1.25 mg/l

  • Total phosphorus as phosphate: 0.11 mg/l

  III. Outstanding waters

  1. Colorado designates selected streams as Outstanding Waters to protect them from degradation.

  2. It applies the status "to certain waters that constitute an outstanding state...resource" [3].

  3. Those streams must "have exceptional recreational or ecological significance" [3].

  4. Hosting Colorado's only native trout species, cutthroat, seems to meet that requirement.

  5. Note that "short-term degradation of existing quality is allowed" [3].

  6. It must result, however, "in long-term ecological or water quality benefit or clear public interest" [3].

  7. This might include activities that reduce wildfire risk or improve roads and trails, for example.

  8. Eight streams or reaches in the study area already have been designated Outstanding Waters.

  9. Water quality was assessed in this study as part of judging whether 9 more streams could qualify.

  IV. Instream flow

  1. Colorado Water Conservation Board (CWCB) may appropriate water rights.

  2. This would be under the Instream Flow Program for reasonable protection of the natural environment.

  3. Eighteen of the study area streams have instream flow protections underway

  V. Sedimentation​

  1. "Discharge that can settle to form bottom deposits detrimental to the beneficial uses" is problematic [3].

  2. "Depositions are stream bottom buildup of materials which include...silt, or mud" [3].

  3. "Beneficial uses" include "the protection and propagation of...aquatic life" [3].

  VI. Nutrients

  1. Nutrient entry into streams, and resulting algal blooms, may occur so long as fecal material from grazing is present.

  2. Dissolved nutrients likely exit with streamflow, but can reappear with recurring snowmelt and rainfall.

  3. That is, nutrient concentrations in streams logically are intermittent, connected with precipitation.

  4. Colorado has set interim water quality standards for nutrient concentrations [3].

  5. Samples from selected study area streams were submitted for nitrogen and phosphorus analyses.

  6. It was part of the 2020 fall season sampling, which was after an extended period of no rainfall.


  1. Code of Colorado Regulations, Water Quality Control Commission, 5 CCR 1002-34, Regulation No. 34, "Classifications and Numeric Standards for the San Juan River and Dolores River Basins."


  3. Code of Colorado Regulations, Water Quality Control Commission, 5 CCR 1002-31, Regulation No. 31, "The Basic Standards and Methodologies for Surface Water."

  4. "Temperature Criteria Methodology," Policy Statement 06-1, Colorado Department of Public Health and Environment, approved 8/8/2011, expires 1/31/2023.

  5. Todd, A. S., M. A. Coleman, A. M. Konowal, M. K. May, S. Johnson, N. K. M. Vieira, and J. F. Saunders, "Development of New Water Temperature Criteria to Protect Colorado's Fisheries," Fisheries, vol. 33, no. 9, pp. 433-443, 2008.

    Background | Regulatory 

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