In early July I''ll be doing a little detour from the "Savonoski" kayak loop to check out Colville lake, and certainly the mouth of the American. I'm guessing the mouth could be anything from a) slow-moving, shallow water and not very fishy to b) a nice "boca fishing" style situation with grayling and bows in the current and char and lakers lurking on the dropoffs.
Later in the year when you're there, covering the whole river, eggs and flesh will probably be deadly, as Norcalbob pointed out.
I'll also be taking a raft down the Alagnak in July with a buddy. You can't beat that area for great fly fishing water
