Broken Bay has its origin at the confluence of the Hawkesbury River, Pittwater, and Brisbane Water and flows openly into the Tasman Sea.

The bay comprises three arms, being the prominent estuary of the Hawkesbury River in the west, Pittwater to the south, and Brisbane Water to the north.

Ray Parkin in his book H. M. Bark Endeavour claims that the modern 'Broken Bay' was passed unremarked at night, and that Cook was in fact referring to the area around Narrabeen Lagoon.

[2] Whatever the case, Governor Phillip was the first non-Indigenous person to examine the present day Broken Bay in a longboat from the Sirius on 2 March 1788.

[4] On 28 November 2005, documentary film-maker Damien Lay claimed that the wreckage of M-24, a Japanese midget submarine involved in the attack on Sydney Harbour in 1942 and disappeared soon afterward, was buried under sand on the seabed, just east of Lion Island.