I'm no corrosion expert, but considering air near the water can cause corrosion, I think even slightly brackish water is going to do a number on a plane pretty quickly.
Geez, you folks leave me with the impression the whole plane is going to crumble to dust within hours just because it was partially dunked.
If that was the case there wouldn't be aluminum hulled boats that still float and there wouldn't planes with aluminum airframes and aluminum floats flying for years on the west coast where I grew up (yes, there's still a bunch of ancient de Havilland Beavers on floats with radial engines plying their trade between the islands out there -- they haven't all been converted to turbines yet). So how do they survive all those decades in air taxi service with all that salt spray coating the airframe every take off.
The key to aluminum's longevity is the stable oxide coating it forms. The volume of the material produced when aluminum oxidizes is the same as the volume of the metal consumed, which is why the oxide layer is stable. Unlike iron or steel, which produces an oxide that has a higher volume and therefore continuously spalls off the surface, thus revealing fresh metal to be oxidized (rust).
Salts will attack the aluminum oxide layer resulting in pits and a white powder material. But that does not happen instantly on contact.
In fact the steel parts in the airplane, if not protected with coatings, are probably more vulnerable.
Nobody knows what primers or coating protections the folks that rebuilt this plane might have used when they so carefully put it back together over 18 years (that HAD to be volunteer effort, not some commercial warbird rebuild shop). We can maybe hope they floated it reasonably quickly, got it to a marina or some place where it could be hosed down with fresh water.
I'm sure we will find out in due course.
