[6] Located near the town of Eden, Twofold Bay is approximately 40 kilometres (25 mi) to the north of the border between Victoria and New South Wales.

The catchment area of the bay is 11 square kilometres (4.2 sq mi) with a volume of 334,559 megalitres (11,814.8×10^6 cu ft) over a surface area of 30.7 square kilometres (11.9 sq mi), at an average depth of 10.9 metres (36 ft);[7] making the bay reputedly the third deepest natural harbour in the Southern Hemisphere.

About 5 kilometres (3.1 mi) south of the islet is Red Point which forms the southern headland of the bay.

[9] Local waters including Twofold Bay are recognised as one of twelve coastal aggregation areas for southern right whales in Australia.

On 7 October 1798 Bass and Matthew Flinders set out from Port Jackson in the Norfolk on a voyage to determine whether or not Van Diemen's Land (now called Tasmania) was attached to the mainland of Australia.

This very accurate survey has required little subsequent modification apart from the addition of water depths and of shore-to-shore distances between important landmarks.

[citation needed] The bay is mentioned in the logs of many ships which sheltered in it from the storms battering that part of the New South Wales coastline.

[12] Quarantine Bay, located 3 kilometres (1.9 mi) south of Eden, is so named because a sailing ship with a smallpox epidemic amongst the people on board took refuge in this (then) isolated area.

[citation needed] In 1843 Benjamin Boyd purchased land in Twofold Bay with the aim of transporting cattle from the district.

Evening: A scene in Boyd Town, Twofold Bay, is the title of a poem by Thomas Fennell, RN, that appeared in a New South Wales literary journal in 1847.