Moose (Alces americanus) will dive in lakes for aquatic plant species despite the fact that there is ample, accessible, nutritious, woody vegetation on land and swimming and diving is a more costly form of locomotion. This behavior used by moose to supplement terrestrial vegetation was a mystery until scientists discovered that aquatic plants are much higher in sodium than terrestrial vegetation and thus serve as the source of this necessary mineral.
[Photo by Devin McHugh caption by Maggie Creamer]
Fraser, D., Chavez, E. R., & Palohelmo, J. E. (1984). Aquatic feeding by moose: selection of plant species and feeding areas in relation to plant chemical composition and characteristics of lakes. Canadian Journal of Zoology, 62(1), 80-87.