OOO and on the other hand, it hardly dawns on me to mention having a water rudder...
(I'm sure John will chime in with his thoughts as well
)
imagine a tricycle gear land airplane.... without a steerable nosewheel. (or a taildragger with nothing but a fixed skid)
they're not a whole lot of fun, especially with a crosswind.
a floatplane is also more likely to 'weathervane' ... if you've got a hard crosswind from the left, that crosswind hits the big surface of the vertical fin and tries to turn the airplane to the left (into the wind).
if you're trying to turn the airplane to the RIGHT, (and without a water rudder) you've got little chance of success.
(and even if you decide, oh heck, I'll just turn to the left instead... the airplane will begin to turn left, till it's pointing directly away from you, and then the wind won't let the airplane turn further)