To the south the coast runs runs 30 kilometres along Cloudy Bay and past the islands and entrances to the Marlborough Sounds. To the north the coast runs 40 kilometres along Palliser Bay, crosses the entrance to Wellington harbour, moves past some Wellington suburbs and continues another 15 kilometres to Makara beach.
Cook Strait is regarded as one of the most dangerous and unpredictable waters in the world. In good weather one can see clearly across the strait. At its narrowest point 23 kilometres (14 miles) separate Cape Terawhiti in the North Island from Perano Head on Arapawa Island in the Marlborough Sounds. Counter-intuitively, at this point the South Island's coast lies further north than that of the North Island.
In Māori mythology, Cook Strait was originally discovered by Kupe the navigator. Kupe followed, in his canoe, a monstrous octopus called Te Wheke-a-Muturangi across Cook Strait and destroyed it in Tory Channel or at Pātea. Other legends: Te Whanganui-a-Tara#Legend of Whanganui-a-Tara.
When Dutch explorer Abel Tasman first saw New Zealand in 1642, he thought Cook Strait was a bight closed to the east. He named it Zeehaen's Bight, after the Zeehaen, one of the two ships in his expedition. In 1769 James Cook established that it was a strait which formed a navigable waterway.
Cook Strait attracted European settlers in the early 19th century. Because of its use as a whale migration route, whalers established bases in the Marlborough Sounds and in the Kapiti area. From the late 1820s until the mid 1960s, Arapawa Island was a base for whaling in the Sounds. Perano Head on the east coast of the island was the principal whaling station for the area. The houses built by the Perano family are now operated as tourist accommodation.
From 1840 more permanent settlements sprang up, first at Wellington, then at Nelson and at Wanganui (Petre). At this period the settlers saw Cook Strait in a broader sense than today's ferry-oriented New Zealanders: for them the strait stretched from Taranaki to Cape Campbell, so these early towns all clustered around "Cook Strait" (or "Cook's Strait", in the pre-Geographic Board parlance of the times) as the central feature and central waterway of the new colony.
Between 1888 and 1912, a dolphin named Pelorus Jack became famous for meeting and escorting ships aroung Cook Strait. Pelorus Jack was usually spotted in Admiralty Bay between Cape Francis and Collinet Point, near French Pass, a channel used by ships travelling between Wellington and Nelson. Pelorus Jack is also remembered after he was the subject of a failed assassination attempt. He was later protected by a 1904 New Zealand law.
At times when New Zealand feared invasion, various coastal fortifications were constructed to defend Cook Strait. During the second world war, two 9.2 inch gun installations were constructed on Wrights Hill behind Wellington. These gun could range 18 miles across Cook Strait. In addition, another thirteen 6 inch gun installations were constructed around Wellington, along the Makara coast, and at entrances to the Marlborough Sounds. The remains of most of these fortifications can still be seen.
The Pencarrow Head Lighthouse was the first permanent lighthouse built in New Zealand. Its first keeper, Mary Jane Bennett, was the first and only female lighthouse keeper in New Zealand. The light was decommissioned in 1935 when it was replaced by the Baring Head Lighthouse.
The shores of Cook Strait on both sides are mostly composed of steep cliffs. The beaches of Cloudy Bay, Clifford Bay, and Palliser Bay shoal gently down to 140 metres, where there is a more or less extensive submarine plateau. The rest of the bottom topography is complex. To the east is the Cook Strait Canyon with steep walls descending eastwards into the bathyal depths of the Hikurangi Trench. To the north-west lies the Narrows Basin, where water is 300 and 400 metres deep. Fisherman's Rock in the north end of the Narrows Basin rises to within a few metres of low tide, and is marked by waves breaking in rough weather. A relatively shallow submarine valley lies across the northern end of the Marlborough Sounds. The bottom topography is particularly irregular around the coast of the South Island where the presence of islands, underwater rocks, and the entrances to the sounds, create violent eddies. The strait has an average depth of 128 metres (420 feet).
The South and North Islands were joined during the last ice age.
The tidal flow through Cook Strait is particularly interesting, as on each side of the strait the tide is almost exactly out of phase so that high water on one side meets low water on the other. Strong currents result, with almost zero tidal height change in the centre of the strait. Yet, although the tidal surge should flow in one direction for six hours and then the reverse direction for six hours, a particular surge might last eight or ten hours with the reverse surge enfeebled. In especially boisterous weather conditions, the reverse surge might be entirely overcome so that the flow remains in the same direction through three surge periods and longer. A further complication for Cook Strait's pattern of current flow is that the tides at the north end have the ordinary two cycles of spring-neap tides in a month (as found along the west side of the country), but the south end's tidal pattern has only one cycle of spring-neap tides a month, as found on the east side of the country.
A colony of male fur seals has long been established near Red Rocks on the Makara Coast, west of Wellington.
In modern times, the strait was first swum by Barrie Devenport in 1962. Lynne Cox was the first woman to swim it in 1975, famously stopping often and diving to the sea floor to collect shellfish and crayfish for her husband. The most prolific swimmer of the strait is Philip Rush, who has crossed eight times, including two double crossings. Aditya Raut was the the youngest swimmer at 11 years. By 2008, 71 single crossing had been made by 61 individuals, and 3 double crossings had been made by 2 individuals. Crossing times are largely determined by the strong and sometimes unpredictable currents that operate in the strait.