The gear oil turns white when mixed with water. This may be a worn seal or a crack in the gear case. You may want to drain all the oil, pump about 7 psi of air into the gear case and submerge in water to look for the leak.
Yes that is definitely water. If it is very milky white then a lower leg unit reseal is in order before it destroys your gears with corrosion and then eventually failure of the lower unit.
Before you go nuts with this buy new seals for the fill and drain plug and refil with fresh oil. This is the most common source of leaks. Check often for water & if it turns white as the others have mentioned follow their advice.
