For more information here is the link http://fraservalleybaldeaglefestival.ca/festival/
The eagles migrate from northern areas when it starts to freeze, the spawned out salmon they feed on are frozen into the ice, and they can't access their main food source. Migration takes a lot of energy and they need to rest and feed when they arrive. They migrate by using thermals to gain altitude and then soar using the winds. Flapping uses so much energy that they would never survive if they had to flap for long distances.
The large gravel beds, formed over 100's of thousands of years at the mouth of the Chehalis River are ideal for spawning salmon, and feeding eagles. The gravel bars are only accessible by boat or hiking, and there is little industrialization or significant agriculture that can disturb the environment. This is also an ideal area for other migrating waterfowl, mallards, swans, snow geese, and Canada geese use the flats.
Taking photos can be a challenge and expensive telephoto lenses are needed to get good close up shots, unless you are in the right place at the right time. Trying to approach the eagles is impossible, because they can see anything on the flats, and they will fly if you get close. Walking the flats can also disturb spawning salmon, and crossing small tributaries can disturb the salmon eggs that have been spawned. The Chehalis flats is slated to become an officially no access area for the time of the year when eagles and salmon are present. It only makes common sense to protect this pristine habitat, so please respect this area and stay off the flats.
There are many eagle nests in the Fraser valley and eagles will be returning to claim last years nests. in preparation for raising young in March. David Hancock who is an eagle researcher does a talk each year for eaglefest and it is worth attending if you are in the area, to find out the latest research on these wonderful birds.
See the link for David Hancocks organization to view eagle cams at nests. http://www.hancockwildlife.org/forum/viewtopic.php?showtopic=114161