Your description sounds similar to the tags they put onto adult steelhead after they returned to the Kalama River hatchery. I caught a few tagged fish on the Kalama in July. The Kalama had a great summer-run return, so the hatchery, not needing the eggs, re-released excess early returning fish at the mouth of the river I believe, allowing anglers additional opportunity to catch them. I turned the tags into the local shop at Mahaffeys. If you remember the number on the tag, you should give the hatchery a call and give it to them.

It looks like your fish dropped into the Columbia and ran up the Cowlitz instead of running back up the Kalama after it was re-released. Straying is natures way of expanding the range of the fish, so most populations have a few percent of its run hardwired to run up other streams. Wandering is also prevalent with summer-run steelhead. In a radio-tagging study in the Snohomish Basin, summer-run fish wandered throughout the Snoqualmie and Skykomish Rivers before returning to the hatchery. Summer-run fish have ample opportunity to wander since they return to streams during the summer, but don't actually spawn until winter or the following spring. Given the opportunity, the fish may have turned around and found its way back to the Kalama. It had plenty of time yet before spawning.