The correct answer is B) entering shallow water at the mouth of a river. When a vessel enters shallow water, such as the mouth of a river, the draft (the distance from the waterline to the bottom of the vessel) will increase. This is due to the Bernoulli principle, which states that as water flows over a surface, the pressure decreases, causing the water level to rise around the vessel. As the vessel enters the shallower water, the water level around the vessel increases, resulting in an increase in the vessel's draft. The other options are incorrect because: A) Discharging cargo would decrease the vessel's draft. C) Transiting from fresh to salt water would have a negligible effect on draft. D) Shifting cargo vertically would not affect the overall draft of the vessel.