I know Chinook and Coho both travel through Lk. WA to get to Lk. Sammamish and then to Issaqquaah Creek to spawn. There is a hatchery on Issaquah Creek. The creek empties out right at Lk. Sammamish St. Pk. If and when they (WDFW) open Lk. Sammamish for Chinook that is the place to be, right in front of the mouth to the creek.

So, ya, it is very likely you may have caught a small salmon the other day.
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Carl C.