Presented by the San Luis Valley Chapter of Trout Unlimited
Upper Rio Grande Basin, Colorado
Premise: The Upper Rio Grande has been in an extended drought for many years. Our water supply has varied widely over the last several years, and the weather has been unpredictable. The current snowpack, coupled with recent weather patterns and long-term forecasts, indicate that 2020 will be a very tough year for stream flows. SLV TU would like to present options and guidelines for anglers to consider, as we all prepare for our summer fishing adventures in the Upper Rio Grande.

General Trout Concerns: Trout are cold water fish that require clean, cold, and well oxygenated water. During low flow periods, stream and lake temperatures often rise above the optimum conditions, resulting in reduced oxygen and stress to the fish population. Additional stress results from reduced available habitat in streams leading to increased disease transmission and competition for limited resources. Anglers contribute to stress levels and increase mortality when catching and fighting fish during these conditions. Responsible Catch and Release angling should only be pursued when water temperatures are 65°F or less!

General Trout Fishing Strategies during a drought:

  • Anglers that intend to harvest trout for food have great opportunities during drought conditions. This group should target waters without special regulations and focus on the fisheries managed as put and take for harvest. These anglers should keep every fish they catch up to their limit without selecting for size if temperatures are higher than 65°F.
  • Anglers that are pursuing catch and release opportunities, should have access to temperature data. That can mean using your thermometer, or by accessing data available on the internet if service is available. Please STOP catch and release fishing at 65°F.
  • Anglers can use elevation and aspect to their advantage in drought conditions. In general, the higher in elevation you are, the better the water temperatures are and the more they are buffered in the 24-hour cycle. Take a thermometer and consider streams on the north side of mountains with lots of streamside vegetation and shade.
  • Early morning is the best time to fish during a drought regardless of where you are planning to fish. There is a myth that stream temps go down in the evening when the sun is set or off the water. This is actually the warmest time of day in terms of stream temperatures.
The example shown below illustrates a typical daily temperature cycle measured on the Rio Grande at the CR-17 bridge on July 15,2018. The lowest temp was at 8:15 am at 63°F. The highest temp was at 2:00pm at 71°F, and the water temp was still 66°F at 10:30pm that night.

What conditions constitute a complete closure to fishing?
CPW has been working state-wide, to develop criteria based on the best available science, that would be used to determine a complete closure to fishing in drought conditions. The information available at this time is draft but is recommended at this time.
Access to fishing should be completely closed if/when:

  • The daily maximum temperature exceeds 74°F
  • The average daily temperature exceeds 72°F
  • Stream flows are 25 % or less than the historical average at gaging locations
  • Fish Fungus is prevalent in the population
  • Daily minimum Dissolved Oxygen levels are less than 5 ppm (parts/million)
  • During events such as wildfire, mudslides, oil spills, etc.
Tools Available to fish responsibly in a drought:
  • Local shops and outfitters. Reach out to the folks on the water every day. Ask them for recommendations on places and times to fish. Stopping by the shop to buy a few flies is preferred but call or visit their websites too.
  • Purchase a reliable stream thermometer (contact one of the shops at the end of the newsletter) and set your phone or watch to remind you to check temps every hour at a minimum.  The SLV TU Board is investigating the possible purchase of thermometers for members – stay tuned or get your own before the summer arrives in earnest!
  • Do your research. Use online tools ahead of time to see what is available to you. SLV TU partnered with the Division of Water resources Division 3 in 2019 to install 5 new temperature sensors on existing stream gages and make that information available online.
Here is a link to environmental data captured at stream gages in the San Luis Valley (water division 3) Division 3 Environmental Water Data

Please consider exploring this website to look for temperature data for other river basins around the state too!

ALWAYS KNOW YOUR FISHING REGULATIONS AND FREQUENTLY REFER TO THEM

Thank You for taking care of your priceless natural resources and public lands!