The head is blunt. Depending on the light, the back may appear black, grey or brown). The flanks are grey and the underside is white. The pectoral fins are black. A dark line runs from the corner of the mouth to the flipper. The more or less triangular small dorsal fin is positioned in the centre of the back. The upper back and dorsal fin are the only features one normally gets to see of a swimming harbour porpoise. The chief characteristics are its small size, the blunt head and the small triangular dorsal fin.