"weather sealed" != "impervious to salt water"

[jhpeterson]

Not to encourage anybody to expose their equipment to salt water, I do have experience in that.
I have been photographing yacht racing for many years using Canon 1D series bodies (1D mkII, 1Ds mkII, two 1Ds mkIII and two 1DX). I have mostly been using the Canon 100-400/4.5-5.6L IS (mkI), which is not (fully) weather sealed, but also 70-200/2.8L IS (mkI) and 70-200/2.8L IS mkII which are weather sealed. When possible I do use UV filters to protect the lenses.
I do try to protect the equipment from water, but sometimes it will be hit by a wave.
Everyday when I get onshore, I wipe all equipment with a damp, clean dishtowel.
I have never had a single failure so far.

One of the events I photographed in 2015 was the World Championship for the Olympic Nacra 17 class (https://www.flickr.com/photos/sailingaarhus/sets/72157655427692796). It was photographed using two 1DX primarily with 300/2.8L IS (mkI) and 100-400/4.5-5.6L IS mkII on the race course.
The weather was quite bad during most of the event. When it was worst I used the Thinktank Hydrophobia rain covers (like https://www.flickr.com/photos/sailingaarhus/18897745314/in/album-72157655427692796/ - at this point the wind was to strong even for these world class athletes). Although the Hydrophobias are excellent, it does make it even harder to photograph these extremely fast boats.
During the final, very intense medalrace, the wind was close to the max limit (https://www.flickr.com/photos/sailingaarhus/19574966062/in/album-72157655427692796/ - the French coaches are cheering as their team approaches the finishing line as World Champions). I had a driver for my RIB boat who could cover me a little. So I chose not to use the raincover, to be able to work faster. But the 1DX with the 100-400/4.5-5.6L IS mkII was soaked in saltwater multiple time (and I dried it with a dishtowel) - the equipment worked absolutely flawless and still does.
By using 2 bodies, I dont have to switch lens - I switch camera. In general I only use one camera at the time.

That's the reason why I, and many yacht photographers, use 1D series bodies.

+1
Having been a yachting photographer for a few decades as well, I fully agree with the above poster.
There's no such thing as a waterproof camera, at least for the way we work. I find myself using a 300/2.8 more than any other and typically complement it with both a 70-200/2.8 and a 500/4. An underwater housing for such long lenses not only would be expensive and impractical, but unwieldy to the point we'd seldom be able to get usable photos.
All I can do is minimize the happening of disasters and mitigate the damage when, not if, it occurs. For that reason I stick to 1D series cameras and weather-sealed "L" glass. A wipedown of every piece of gear with a cloth dampened with fresh water then dried with a towel is mandatory after getting ashore.
I've use raincovers when the seas were the worst. While they slow down my work, they do provide one more level of protection, which may mean my gear keeps working in conditions where it may not have otherwise. Perhaps it even lives to see another day.