The Tank Stream - ABC Online

It is probably one of the first history topics Sydney school students learn about - that after arriving at Botany Bay in 1788, Captain Arthur Phillip made the decision to move further along the coast to Port Jackson in order to be close to a source of fresh water.

The stream became polluted and unusable within just a few decades of European settlement, even though the local Gadigal people had maintained a healthy stream for thousands of years prior.

Yvonne Kaiser-Glass, Adviser in Heritage for Sydney Water describes the stream today as still being a powerful resource, ""The Tank Stream no longer works as a fresh water supply but as part of the storm water catchment,"

"The flow alters all the time so the stream has many moods, we saw it at a particularly low flow period today but in previous times when rain has moved into the catchment, we've closed the (entry) hatch and you can hear what sounds like a train pulling in to Wynyard. It's like a submarine hatch and once we close it, it's safe and turns back into a secure system, but the sheer volume of water rushing through there can be phenomenal."

"The Tank Stream starts at Hyde Park and ends at Circular Quay - it's a drop of 30 metres. Now it's on a harsh rock floor but back then it was a drop of 30 metres over a series of waterfalls so it was a really beautiful environment. Because it is the lowest part of Sydney's CBD it still works perfectly as a storm water catchment area."

Originally just the fresh water source, within 40 years work was well underway to cover the Tank Stream with sandstone blocks as a result of it having become a sewer flowing into the harbour.

The city of Sydney has grown up around the Tank Stream, now placing the stream essentially underground. The construction methods and materials that now enclose the Tank Stream vary considerably from large sandstone blocks over quite a wide tunnel to a very narrow oviform brickwork duct.

Jon Breen, Heritage Engineering Archivist for Sydney Water, points out changes in the structure of the tank stream and also an area that remains wet which is from the original spring from which Spring Street gets its name.

"That's special because it's the spring from Spring Street and although this has all been built over it, the pressure from that spring is still enough to go under the rock and bubble out at that point."

Many thousands of people enter the ballot for tickets via the Historic Houses Trust but only a few hundred are able to join one of two tours each year.