Like nearly all vertebrates, the salmon is an excellent osmoregulator. However, like virtually all osmoregulators, the salmon is never in true equilibrium with its surroundings. As you can see from Row #1 in the accompanying table, in the ocean, the salmon is bathed in a fluid that is roughly three times as concentrated as its body fluids, meaning that it will tend to lose water to its surroundings all of the time. And, because the composition of its body fluids is so different from the ocean water, the salmon will be faced with all manner of gradients that are driving exchanges that will continuously tend to drive its body fluids' concentration and composition beyond homeostatic limits. In particular, the very high concentration of NaCl in the ocean water relative to its concentration in the salmon's body fluids (see Row #2 in the above table) will result in a constant diffusion of NaCl into the salmon's body. Unless dealt with effectively, this NaCl influx could kill the salmon in a short time. In sum, a salmon in the ocean is faced with the simultaneous problems of dehydration (much like a terrestrial animal, such as yourself) and salt loading.