Check flows, and the Water temperature too!

Flows out of Foster Reservoir dropped this week, and the change brought the South Santiam River into an ideal range for fly fishing for hatchery summer steelhead anywhere from Foster Dam downstream to Waterloo Park.

The graph above shows the abrubt drop in stream flow just below Wiley Creek.

Knowing from past experience that flow is not the only factor that is likely to influence the steelhead’s tendency to be catchable on flies here, I dug one layer deeper into the Real Time Streamflow Data.

Here is where one must dig to get a larger picture. Instead of scrolling straight down to the flow on this page, examine the box listing Available Parameters for this site. If it gives the option for a specific river, go ahead and check the Water Temperature box, specify the duration in days, up to 30, and hit the Go button.

Ahah! Just when the flows were reduced to a highly fishable flow level, the temperature dropped and dropped drastically. Instead of a 50 – 52 F daily water temperature cycle, we have, for the present anyway, a chilly 40 – 43 degree F cycle. This probably means that when the flows were choked down, the spill was drawn from a cooler deeper layer in the reservoir, or some different mix of surface and subsurface layers.

Such changes in the mix of surface and subsurface waters the Corps spills may, at times, be managed in order to accomplish a variety of objectives, including but not limited to: accelerating downstream migration of smolts, increasing the opportunity for naturally produced steelhead and spring chinook in the reservoir to find the outlet and migrate downstream through the dam, keeping the Willamette a tad cooler in the heat of the summer, and keeping temperatures cool during the spring chinook spawning period in the fall.

Main point here, is that when possible, it makes sense to check those water temperatures as diligently as the flows. A sudden change to 40 Degree F water can put steelhead in a dour mood and make the use of a big fly drug across the bottom a good idea. I have seen similar changes when the water went from the low 40s to the mid 50s, and this was potentially the trigger for some of the best summer steelhead fly action I have ever had on the South Santiam.

Hope this helps.


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3 Responses to Check flows, and the Water temperature too!

  1. Guy says:

    Good advice Jay…and it explains why i’m fishing a skagit W/ 10′ of T-8 in summer,
    yesrerday was a nice drop for the S. Santiam’s evil twin !

  2. Oregon Fly Fishing Blog says:

    Right on. The South Santiam, for all the reasons noted, is notorious for cold water in the heat of summer. Daily variation in temperature is sometimes just a few degrees F with afternoon peaks around 3-7 PM, which may explain why late afternoon and early evening fly fishing is sometimes more productive than morning. Conversely, the flows may remain fairly constant during summer, but water temps can make a big jump up if the Corps draws water from a surface layer, so it always makes sense to check before you go fishin’ here. JN

  3. roy humphrey says:

    talked to brett at the foster hatchery fishing today! he said water temp dropped and it was 50degrees! trying to locate were that is recorded. and how it happens when the levels are just dropping slightly? good idea to move smolt and cool the willamette but i do not get how it happens???? help

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