The sea mink was the largest of the minks. As only fragmentary skeletal remains of the sea mink exist, most of its external measurements are speculative and rely only on dental measurements. In 1929, Ernest Thompson Seton, a wildlife artist, concluded that the probable dimensions for this animal are from head to tail, with the tail being long. A possible mounted sea mink specimen collected in 1894 in Connecticut measured from head to tail and the tail was in length; a 1996 study found this to be either a large American mink or possibly a hybrid. The specimen was described as having coarse fur that was reddish-tan in color, though much of it was likely faded from age. It was darkest at the tail and the hind limbs, with a white patch between the forearms. There were also white spots on the left forearm and the groin region.