Is the Apple Watch waterproof?

Update (09/12/17): The Apple Watch Series 3 available September 22 is listed as “swimproof.” The fine print on apple.com notes that the Series 3 Watch is water resistant up 50 meters under ISO standard 22810:2010. This means it is safe to take your watch in swimming pools or the ocean, but it should not be used for scuba diving, water skiing, or other water activities where it may be submerged in deeper water.