Sydney Harbour is so deep because it's a "drowned river valley," a natural feature where the sea flooded ancient, steep-sided river channels carved into sandstone over millions of years, creating deep, sheltered waterways ideal for shipping. The powerful currents and wave action around headlands prevent sediment from filling these channels, maintaining their depth, and areas near the mouth of the Parramatta River are particularly deep due to strong water flow.
Sydney Harbour is the deepest natural harbour in the world with 504 billion litres of water. It spans approximately 240 kilometres of shoreline. There are over 586 species of fish in Sydney Harbour. These include Bull Sharks, White Sharks and Tiger Sharks between 2 and 3.2 metres long.
10 secret Sydney spots you might have all to yourself
New lead-free paint applied to steel on the bridge protects it from the atmosphere and limits rust from forming.
Most Sydney Siders will advise you not to swim in this water as the murky water makes it a prime breeding ground for bull sharks and jellyfish. However, further upstream where the water becomes fresher and clear it is ideal for a swim.
Previous test results have revealed elevated levels of dioxins in fish and crustaceans across Sydney Harbour, including Parramatta River and other connected tidal waterways. A ban was consequently placed on commercial fishing in 2006 as a precautionary measure.
Sharks are found all around Australia, but hotspots for diversity and activity include the Coral Sea (Queensland) for biodiversity, Western Australia's South West (Geraldton to Victoria) for great whites, and the NSW/QLD coastlines (like Byron Bay/Ballina) for higher shark attack numbers, often linked to bull sharks and river mouths. Major populations of great whites are concentrated in WA's waters, while the warm Coral Sea teems with many species.
It's easy to see why Sydney Harbour is regarded as one of the most beautiful natural harbours in the world.
On 15 October 1970 at 11.50am, a section of the West Gate Bridge known as span 10-11 suddenly collapsed and fell 50 metres. The bridge had been under construction for two to three years. In total, 35 workers died as a result of the collapse.
Some say once every seven years, others say from end to end each year. The truth is that the Bridge is painted continuously.
Fortune of War – Sydney's Oldest Pub | The Rocks, Sydney.
It may be home to its fair share of Australia's icons, but Sydney is still full of surprises. Laneway bars, sunken gardens, and ocean baths are just a few of the quirky secrets hiding in Sydney. If you think you've seen and done it all, it's time to think again.
The series follows the story of an emotionally turbulent teenage girl, Sydney Novak (Lillis), who discovers that she has psychokinetic powers that are triggered by strong emotions. As the series progresses she aims to gain control over her powers while navigating the complicated relationships of her life.
Did you know that Sydney Harbour is an Estuary? Like all Estuaries, the Harbour is a mixing place of saltwater from the ocean and freshwater from the rivers.
The Most Beautiful Harbour in the World - Sydney Harbour.
The route winds along parts of the foreshore, into bays and on to headlands, through the bush, along historic streets and over grand bridges. The Circle Walk can be walked by a fit person in approximately eight to ten hours, but with little time to savour the sights along the way.
The 11 November 2025 landsldie at Hongqi Bridge in Sichuan Province, China. A large landslide has destroyed a 662 m long highway viaduct in China. Over the last two days there has been considerable media coverage of a large, highly destructive rockslide that occurred at Hongqi Bridge in Sichuan Province, China.
The oldest surviving European structure in Australia is the Wiebbe Hayes Stone Fort, built around 1629 by shipwreck survivors on West Wallabi Island, WA, but for intact colonial buildings, Elizabeth Farm (1793) in Sydney's Parramatta is widely considered the oldest house, while Old Government House (1799) in Parramatta is Australia's oldest public building, both offering glimpses into early settlement.
The Hussaini Hanging Bridge, in the beautiful Hunza Valley of Gilgit-Baltistan, Pakistan, is known as one of the world's most dangerous bridges. It hangs over the Hunza River and connects the village of Hussaini to the other side.
What is now Sydney in the last ice age was 120 metres above the shoreline. When those glaciers melted 12,000 years ago – what is now Sydney Harbour was a river valley that was drowned. The water flooded in and the water level rose 120 metres.
Water quality in Sydney Harbour
Sydney Harbour is remarkable compared to most working harbours near large cities as it hosts a great diversity of marine life and is safe for swimming in many locations.
To tell if a shark is near, watch for nature's signs like diving birds or agitated fish, notice unusual shadows or fins, and be aware of areas with fishing activity, but most importantly, listen to lifeguard warnings, avoid murky water, and observe sharks' behavior for signs of excitement or erratic movements, indicating you should calmly leave the water.
Thus, sharks see the underwater world in shades of grey and, rather than being attracted to a particular color, they are probably attracted to what humans think of as yellow simply because it is a bright object against the darker background of the water.
After Dutch navigators charted the northern, western and southern coasts of Australia during the 17th Century this newly found continent became known as 'New Holland'. It was the English explorer Matthew Flinders who suggested the name we use today.