Depends on the stream. On some of the larger tribs, don't be surprised if you catch fish all the way into mid/late May. Some folks have some success catching Skamania strain summer-runs on the Salmon River in June and July, even August...

This year people have been catching a lot of drop-backs - as early as November - on some Erie tribs, and probably Ontario tribs as well. The funky weather definitely got some fish all whacked out, with warmer water and higher flows like they'd usually see during spring time. But you'll still see good numbers of fish in medium-to-large tributaries in April and early May.

If you're wondering how late you can get away with a successful steelheading trip, I'd say your best bets would be Cattaraugus Creek (Erie), lower Niagara River (Ontario), Genesee River (Ontario), Oswego River (Ontario), and Salmon River (Ontario). I'm sure there are some good-sized Erie tribs in Ohio that will also have enough base flow to keep the water cool and high into May (Chagrin, etc.).

If you manage to get out during late Feb/early March, you'll have the opportunity to get into some wintered-over browns in the western Ontario tribs along with good numbers of steelhead. Generally the shelf ice is gone by then and the fully iced-over streams are opened up.

Marty