Hi,
I own a similar Keen shoe and the answer is they are waterproof. i.e.
you will not damage the shoe by submerging in water. They do not
however dry instantly and if you wind up with sand in them as I do
they become uncomfortable until they are cleaned and dry again. If you
are boating and portaging, they are probably a good choice. If you are
only boating many of the neoprene booties or socks are probably better
since they keep the grit out.

Gene

Thanks Gene!

I can see how the sand would get "trapped" in them and
make them uncomfortable.