Sammy Today discovered an SM-G850F, saying that this is supposed to be an international variant of the S5 Active. The SM-G850F already has support pages at Samsung Norway, Samsung Sweden, and Samsung Finland. Unfortunately, the support pages only mention the smartphone’s model number, without providing images or other details.
The S5 Active should have the same 5.1-inch 1080p display of the regular Galaxy S5 (pictured above), but it might be a bit larger overall - possibly because it has a rugged body and extra protection against water.
Samsung could announce the Galaxy S5 Active in the near future, but that's just a wild guess.
source: Samsung (1), (2), (3) via Sammy Today