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.