I have caught steelhead and large trout, as in trout up to 4 lbs, in the slough but that was when you could fish for coho in the fall with bait and issaquah creek still got a good number of steelhead in the winter. The trout would follow the salmon upstream to feed on their roe, which probably still happens.
I haven't fished the lake for quite a while ,but 30 years ago ( damn how did that happen) we caught a lot of those pike minnows while pitching crankbaits for smallmouth bass. Some of them where pretty large. I have know idea about population fluctuations in lake washington, but the book, Inland fishes of washington, has some pretty good life history info.
Approximately 55 years ago a certain boy of about ten was going fishing on opening day with his dad. A special lake which had received reports of great fishing was to open. Alas, the road approaching the lake was jammed with so many cars that the dad decided to just go to Lake Sammamish 'cause it's open all year. The little boy was more than disappointed. He was really looking forward to the new hotspot, and by the time they reached Sammamish and launched, the morning would be half over! Well, dad put up with the sons pouting and put a Dick Nite spoon on the boys line. With plenty of coaching, the boy landed a five pound rainbow, got his picture in Fishing and Hunting News, and received a card full of spoons from Dick Nite. (and never again questioned his dads advice)
In my late 20's/early 30's and family would head off to Holy Cross in Redmond Washington. They in 'best bib and tucker' and me in fishing clothing. Wife would drop me off at Marrymore and I'd fish my way back to Bothell. Bobber/jig/10 foot rod .... sometimes I got lucky.
Then the luck changed ....... New Priest and one heck of a fellow (as were his wife and 5 kids-theirs, adopted, foster). Anyway hit the SS at about 8AM and Bam! like on the third cast. Fish on beach, cleaned and in the cooler. 30'ish minutes later: BAM! Second fish on the beach, cleaned and in the cooler.
Half hour later and, you guessed it, BAAAAM! And I had my three fish limit. Then off to church and I was scratching my head as to what to do with at least two of the fish so I asked Father Todd's wife if she'd like two of them. YES WE WOULD!!~!!
About 3PM I get a call from her asking how she should cook them and I responded (to the effect) 'Just like you'd do a whole Salmon.' Dead pause for a few seconds: 'We've never been able to afford to buy one." Gave her the instructions how to wrap in Allie Foil, veggies, etc., about as simple as you can get.
Next Sunday the whole family was all over me about how much they enjoyed the fish, etc., etc. Looked at Father and said: 'I'm good at pitching, you're good at Praying, how about we split the catch?' (Actually if only one, they got it. And it was rare that I didn't have at least one, but it did happen.)
Never before, or since, have I had a winter fishing season that even came close to that one. "Shooting fish in a barrel' time for the next 60 - 90 days. Father Todd? He retired as a leading Bishop in the Episcopal Church (Southern California if memory services).