I looked into this a little more myself and found the following useful information:

What if the current property owner's deed reads to the middle of a river, or seems to surround and include the river?

If the physical characteristics of the river are such that it meets the federal test of title navigability, it is public land up to the ordinary high water line. Since a deed can only convey interests actually owned by the seller, and since the bed and banks of all navigable rivers passed to the states at the time of statehood, it is likely that the state is the true owner. The state's ownership is a "prior existing right" and is frequently mentioned as such on deeds. Somewhere along the chain of property transactions, a deed may have been changed to include the riverbed. Unfortunately, if this happened it was likely done incorrectly. In some states the property owner next to a river may have certain rights, such as the right to construct a small dock that extends onto the public land at the edge of the river. Note that a determination that a river is navigable for title purposes is not a "taking" of private property under the U.S. Constitution-the river and the land along it were public land all along. A "taking" can only occur if the land in question was clearly privately owned in the first place.

http://www.adventuresports.com/river/nors/states/wa-law.htm