The kidneys of a dolphin are large, consisting of numerous interconnected and closely packed lobes called "renculi". Similar forms of renculi have been found in other marine animals but there is yet a known reason for the existence of this structure. There is a possibility that the presence of these lobate kidneys is part of the adaptation of the dolphins' underwater life.
Dolphins have to obtain their supply of water despite living in the sea as the water in the sea is saline and not suitable for consumption. Dolphins get most of the fresh water they need by eating fish. The kidneys are not very specialized in desalinating water. Instead, the dolphin's skin does most of the job by acting as an osmostic membrane, allowing only water but not salt to enter its system. However, the dolphin's kidneys are not entirely useless - they contain special structures which may aid with filtration during diving.