If you are having trouble working out the picture, it's a screen grab off google earth. The white area is a southerly swell breaking on shallow coral reef. The pale blue area slightly off centre is a sand hole in the reef in about 5m of water.
The sand hole first started to form 381 years ago today, when on her maiden voyage the VOC ship, the Batavia, ran aground on a moonlit night with little swell. The watchman mistook the surf for the moon's shimmer and the ship rammed into the reef under full sail. Half a mile either way and they would have sailed clean through the Houtman Abrolhos without ever realising. As it was, the pride of the Dutch fleet was doomed to break up on Morning Reef over the next week or so. The already mutinous crew and terrified passengers were either, ferried on the ship's longboat to nearly islands, which were sandy cays at best, or drowned trying to swim there. Some non swimmers stayed on the broken ship drinking the liquor and parading the deck drunkenly in the captain's finery, before belatedly drifting ashore some days later, with the rats, on the spars and rigging of the 600t ship.