Free: Contests & Raffles.
I don't think you ever "have to keep" fish. There is a rule (check regs.) that says if you are using bait (where legal) for trout (other than steelhead) the first 5 fish (where 5 is the limit) will count toward your limit whether you keep them or release them. This is because trout caught on bait do not generally survive well when released. It is one of the more ignored rules IMO.
Taking the kids here this weekend, never fished it so I did a search here for some pointers on what works and noticed that someone said the limit is 5 and you have to keep the first 5 you catch. I didn't see this in the regs under Riffe lake, is this a park rule? I'm the only 1 in the family that eats fish and I don't eat a lot, we mostly catch and release, Am I going to be stuck with 30 fish if we limit both days? , if so, kids cat should be happy.