Rainbow trout don't live long enough to attain 3 foot lengths unless they are able to spawn or are steril. In lakes and res that is. Certain strains are able to attain that weight in large bodys of water where the have ample fish to forage on ( like priest lake or others in that area) Also some large ones ( browns) in the great lakes. Fish that don't spawn, have to re-absorb their eggs, and a couple of years of that and it kills them. A brown trout will live much longer and can reach that size..

Remember, I am not talking about steelhead, I am talking about your avg rainbow trout.