Although the success of compliant walls in mimicking dolphin skin is well known, the drag-reducing properties of a dolphin's skin are still unclear. Moreover, little is known about the relation between the 3D structure of the skin and the local flow conditions. To study the role of a dolphin's skin in reducing the drag the skin morphology parameters were compared with the parameters of an anisotropic compliant wall and a possible flow–skin interface was considered. The 3D structure of skin from different locations was modelled using serial histological sections of the skin. The hydrodynamics of the dorsal fin of the harbour porpoise was studied by means of computer simulation of the flow around virtual models of the fin. It was found that the distribution of the skin morphology parameters is correlated with the local flow parameters on the fin surface. The skin structure appears to allow the flow–skin interface to behave similar to an anisotropic compliant wall in the regions of favourable and adverse pressure gradients on the fin. The relation founded between the skin morphology and the local flow parameters could be useful in the design of multipanel anisotropic compliant walls.