I've done lots of bald eagle trips.  Prime time is usually right around New Years up until about the middle of Jan.  By the middle of Feb most of the eagles are gone.  I'd say from the middle of Dec to the middle of Jan is the best time.

 Also, consider doing the Upper Skagit instead of the Marblemount to Rockport section.  The Upper Skagit won't have as many eagles but the setting is much more intimate.  You won't see many other people and there are no motor boats powering up and down the river.  Also there are people and houses everywhere on the Rockport section. 

Can you tell that I have become disenchanted with the Marblemount to Rockport section?  It does have the sanctuary which adds to the eagle count but its so dissappointing to me due to the number of fisherman with motor boats, tourists, and rundown homes along the river.

Its absolutely absurd that the forest service has a rule that no rafter sor kayakers are allowed to put in at Marblemount before 11 so we don't disturb the eagles feeding while there are about 20 motor boats powering up and down the section starting at daybreak.....

I was actually planning to take a raft, but from the sounds of it I might have to nix this one until next year.

The whole point was to take a few older friends down a mellow float looking for eagles and photo opps. Thanks for the beta, that probably saved me a trip right there! I had no idea it was so much earlier in the season.

I agree with Horner on all points.

I did a trip there 2 weeks ago and there were still a few eagles but not like in the prime of the season. The eagle migration to the Skagit is timed with the chum salmon run which is in Dec-Jan. Once the salmon are gone, the eagles move on.

Usually the best time to see alot of eagles is on a cloudy day, as they stay close to the river then. On bright, sunny days they will be up soaring high... which is cool to see too, but you don't get so many close ups.

Be sure to spot out all the different species of Eagles to your passengers too. I always point out the dwarf eagles (crows) and "white eagles" (you can probably guess what those are)

Also people should know that you will be charged to take out at Howard Miller Steelhead Park which is baloney.

A few weeks ago we counted 35 on the way up 542 to Baker, a week after the flooding they were all gone, now I'm lucky if I see 2 or 3 on the way up. I've seen more earlier in the winter than later but there's always some around.