A Swimmer can cross Rivers, which sometimes mark the boundaries of provinces. While some boundary-marking Rivers have bridges across them, quite a few crossings require either ice, Flying, Floating, Water Breathing, or Swimming to cross.

A Swimmer is also better Underwater than a Water Breather and a Poor Amphibian, since swimming is much easier than walking along the bottom of the ocean. However, the Swimming trait does not let you breathe water, so Underwater combat will require one of the two "lesser" water-breathing traits; as for why this is the case, air in the lungs will make even reaching the bottom of the ocean very difficult. Aquatic beings and proper Amphibians are already good Swimmers, so the Swimming trait is completely redundant on them.

Swimmers cannot cross Seas in the same manner as Sailors, though they may (of course) ride alongside them if they aren't Commanders.