washed downstream?

[shirfan]

803.03F states: A disc thrown in water shall be deemed to be at rest once it is floating or is
moving only by the action of the water or the wind on the water.

This, I assume, means that if a disc is thrown into a creek and washed several hundred feet downstream, it is to be played from where the majority of the group last spotted it above dry ground, with a one-stroke penalty.

However, if the stream is previously ruled casual, what then? Should it simply be played from the bank away from the basket where it was last above dry ground, with no penalty? What if it entered the water behind a pine tree, blind to everyone at the tee? Majority-rule estimate of where it landed?

[Dogma]

Casual water that has enough flow to carry a disc several hundred feet? Had some rain recently?

shall be deemed to be at rest once it is floating or is moving only by the action of the water or the wind on the water.

Doesn't look like this rule discriminates between casual and non-casual water. You play from where it went in/over the water.

As for how to determine the location, the OB rule is:

"B. A player whose disc is considered
out-of-bounds shall receive one penalty
throw. The player may elect to play the
next shot from:
(1) The previous lie as evidenced by the
marker disc or, if the marker disc has been
moved from an approximate lie, as agreed
to by the majority of the group or an
official; or (2) A lie that is up to one meter
away from and perpendicular to the point
where the disc last crossed into out-of bounds,
as determined by a majority of the
group or an official. This holds true even
if the direction takes the lie closer to the
hole;"

Based on that, I'm guessing majority rule would apply to the situation you described too, even though it isn't technically OB. Same as choosing an approximate lie for a lost disc, disc played be wrong player, etc.