Mercury Bay is an inlet on the east coast of Coromandel Peninsula, part of a drowned valley system divided into two portions, the outer one of which is Mercury Bay and the inner one, a south-western extension of the indentation, Whitianga Harbour or River. The point of division is the strait-like Narrows linking the expanse of Mercury Bay with Whitianga Harbour. On the southern side of the Narrows the prominent Whitianga Pa (or Whitianga Rock), at one time ringed with stone terraces and strongly fortified, rises from the water. Whitianga, principal settlement of the locality, is situated on the northern shore of the Narrows, at the southern end of Buffalo Beach which sweeps northwards and eastwards to the northern head of Mercury Bay. In the southern portion of Mercury Bay, about 2 miles east of Whitianga, is the 2-mile strand of Cooks Beach, bounded at the western end by a bluff headland terminating in Shakespeare Cliff.

The locality has many historic associations. Captain Cook arrived in the Bay in November 1769, at once set up his shore station at Cooks Beach, and, on 9 November, observed the transit of Mercury. On 15 November the British flag was hoisted and sovereignty for Great Britain was claimed by Cook in the name of George III. During the early 1830s an important kauri “spar station” was established at Mercury Bay by Ranulph Dacre and for some time was managed for him by Gordon Davis Browne. The kauri timber and, later, the kauri gum industries flourished for many years. In 1919, on the erroneous assumption that Cook's observatory had been sited on Shakespeare Cliff, steps were taken to acquire the land as an historic reserve. Accordingly, in the early 1920s, some 88 acres were set aside there and a monument erected to commemorate Cook's visit. Today the beaches around Mercury Bay are popular summer resorts. One of them is called Buffalo Beach after HMS Buffalo, which went ashore in a violent gale on 28 July 1840 with the loss of two of her company. The bay is also a base for deep-sea angling in eastern Bay of Plenty waters.

The bay was named by Cook. To the ancient Maoris it was known as Te-Whanganui-o-Hei, the great bay of Hei.

by Susan Bailey, B.A., Research Officer, Department of Industries and Commerce, Wellington.