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  A. Introduction

  1. Drought in 2018 produced the Dolores River's second lowest flows in nearly 70 years.

  2. What water temperatures resulted? Trout require cold water.

  3. How do 2018 summer water temperatures compare with the applicable Colorado criteria?

  4. What about 2019 and 2020 temperatures?

  5. Where might trout find refuge from water that is too warm?

  6. What are 2020 and 2021 water quality conditions? How do they compare with Colorado standards?

  7. Do findings speak to how trout populations may survive despite changing climate?

    Background | Regulatory 

Mid-July flow at Bear, a habitat-resilient tributary


  B. Setting

  1. The study area, which is mountainous, is a 500-sq-mi basin in southwest Colorado.

  2. It rises from 7000 ft at the town of Dolores, flanked by McPhee reservoir, to approximately 14,200 ft.

  3. It hosts at least 42 perennial, trout-bearing streams, 240 miles in total length.

  4. They drain into the Dolores River, which is approximately 60 miles in length.

  5. Watershed characteristics for each of the 42 streams are shown here.

  6. Water temperatures were measured in July-August 2018 at 22 main stem and tributary sites.

  7. They were measured at 11 main stem and tributary sites in 2019; and at 6 tributary sites in 2020.

  8. Water temperatures measurement locations and results are shown at Maps.

  9. Water quality samples were collected for analysis from 12 tributary and main stem sites in July 2020.

  10. They were collected from 10 sites in September 2020 and from 8 sites in January 2021. 

  11. A video of water sampling shows sample collection, describes handling, and identifies analyses.

  12. Water quality sampling locations and results are shown at Maps.

  C. Collaboration​

  1. Dolores River Anglers (DRA) collaborated with San Juan National Forest (SJNF) in selecting sites.

  2. DRA is a local chapter of Trout Unlimited (TU); SJNF is a district office of the U.S. Forest Service (USFS).

  3. DRA and individual members supported sensor purchases, placement, and data downloading.

  4. SJNF shared equipment and assisted with sensor installations and data downloading.

  5. There was funding from Colorado Water Conservation Board (CWCB) and Colorado Trout Unlimited (CTU).

  6. Mountain Studies Institute (MSI), funded by Pew Charitable Trust, providing water quality analyses.

  7. Analyses also were supported by DRA as an organization and by a DRA member.

  8. Selection of streams for water quality sampling was made by DRA, in coordination with MSI.

  9. DRA members performed the sampling and the field measurements at those streams.

  D. Comparison​

  1. The water temperature measurements were compared with Colorado criteria for CS-1 streams.

  2. See Criteria, Data, Plots, Findings, and Interpretations. See also Regulatory environment.

  3. Water temperatures were collected continuously at 30-minute intervals.

  4. They were converted to weekly average temperatures (WAT) for comparison with the CO chronic criterion.

  5. And were converted to two-hour average temperatures (TAT) for comparison with the CO acute criterion.

  6. pH and dissolved oxygen were measured onsite.

  7. Other non-metals and the metals analyses were performed on samples delivered to a laboratory.

  8. Analysis results were compared with Colorado water quality standards.

  9. See Criteria, Non-metals and Metals results, and Findings.

  10. See Gallery for views of sensor equipment and installations, and site flow and streambed conditions.

  11. Reports, presentations, databases, regulations, and other information about to the study are here.

    Background | Regulatory 

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