Actually, kayakers are quite easy to spot when landing. Being above
the lake gives one an excellent perspective and allows you to see very
small boats that may be tough to see from another boat (as a kayaker
myself, I'm far more worried about drunk powerboaters who aren't
looking out or can't see me because of the structure of their boats
than I am about seaplanes - I also know that the pilots really, really
don't want to hit anybody or anything because the aircraft structure is
light enough that it's going to come out the definite loser). Keep in
mind that there is no voodoo to being "above" something, you don't
suddenly become blind, you actually have a better perspective. It's
like the lifeguard at the beach on the elevated platform, she or he can
see the swimming area far more effectively than at or close to water
level. On landing I can also see the kids in the inner tubes or
floats, right on the surface of the water, or swimmers who have decided
to swim across the lake, that I would have a heck of a time seeing from
a boat sitting on the surface. (That's why ships used to have a crow's
nest, so the lookout could things that couldn't be seen from the deck.)

"Close" is an opinion. For example, I will land a seaplane at a right
angle fairly "close" behind a powerboat that is going away from me to
my left or right, because his distance from me is increasing and even
if he stops, we still have adequate separation. If the boat is
converging with my course, I'm going to stay a long ways away, because
the boat may very well be faster than my airplane. As to a kayak or
canoe, "close" is looked at in two ways - 1) I do not want to land
close enough to the kayak or canoe that my wake (even though it is
pretty small) will cause a problem or that I will scare the boater, so
I'm going to establish a path that lets the boater predict where I'm
going and that I'm not a threat to him and 2) far enough away that even
if the boater starts paddling for all he or she is worth, the boat
can't possibly get close enough to me that there is any risk of
collision. An onlooker, hampered by the foreshortening of distance
from the surface, may come to the conclusion that the airplane and the
boat are far closer than they actually are. It's like watching the
horse teams or drill teams from the perspective of the viewing stand,
the people or horses pass each other with plenty of distance for
safety, but the angle of the viewer makes it look much closer than it
is.