It is closed (defined as "no fishing of any kind") to salmon/steelhead fishing above marmot dam all year. In the WIllamette zone all steelhead/salmon fishing is closed unless specifically noted in the specific stream regulations. It is a little difficult to understand. Just like, no bait can be used for trout fishing unless noted in the specific stream regulations. Last summer during opening trout season I saw no less than 12 people in one small area using worms and eggs for trout on the salmon river above marmot. Obviously, they didnt understand either. The cops were out in force giving tickets. Bottom line, if you have a pole in your hand outside of trout season (April 26 - Oct 31)....TICKET. If you have bait while fishing anytime, all year long...TICKET.
Hope this helps. See regs below.
2003 Willamette Zone Regs