The name Tasman Bay is generally applied to the broad triangular indentation, approximately 47 miles across and 35 miles deep, in the northern coast of the South Island between Separation Point and D'Urville Island. The bay was discovered by Tasman in 1642, but was not named. In 1770 Captain Cook referred to the whole bay between Cape Farewell and D'Urville Island as Blind Bay, but on his second voyage in 1773 restricted Blind Bay to the part between Separation Point and D'Urville Island.

d'Urville in 1827 was the first to use the name Tasman Bay for the same feature and he specifically fixed Separation Point as its western boundary. Blind Bay is still used occasionally as an alternative name for Tasman Bay.

The inner portion of Tasman Bay is extremely shallow – less than 20 fathoms – but the outer portion reaches a depth of over 50 fathoms. The bay was probably formed during the early Pleistocene glacial period, when thick gravels were deposited in the Moutere depression extending south from the head of the bay, and when sea level may have been as much as 50 fathoms lower than at present. The chief ports in Tasman Bay are Nelson, Mapua, and Motueka. Of these, the port of Nelson is by far the most important, being accessible to all vessels except those of very large tonnage. Although there are no recognised port facilities along the east side of Tasman Bay, numerous inlets and bays – such as Croisilles Harbour, Greville Harbour, and Port Hardy – afford safe anchorage to shipping.

by George William Grindley, M.SC., New Zealand Geological Survey, Lower Hutt.