"I feel that my brain is suffering and I am in great fear of what effect all this worry may have upon me — I have lost control of my thoughts."

Hidden in a vault at the State Records Office is the suicide letter of one of WA's most towering figures — the state's first engineer-in-chief, CY O'Connor.

Best known for developing Fremantle Harbour and for the Goldfields Water Supply Scheme (often known simply as the Goldfields Pipeline), it was the latter project that drove him to despair.

Constriction of the pipeline from Mundaring to the Goldfields was finished in 1903. ( Supplied: National Trust WA )

The Irish-born engineer took his life before the construction of the 560-kilometre pipeline — designed to pump water from Mundaring to the booming Goldfields hub of Kalgoorlie — was complete, after enduring unrelenting criticism.

He wrote the letter on March 10, 1902, the same day he rode his horse past Fremantle Harbour, south to Robb Jetty, then into the sea to take his own life.

While he had given up hope, he had not given up on his dream of a pipeline, providing final instructions as a footnote to his suicide letter.

"Put the wing walls to Helena Weir at once," he wrote.

State Records Office senior archivist Damien Hassan said the letter, which formed part of the inquest records into O'Connor's death, was a deeply sad but historically significant document.

O'Connor's suicide letter is one of the fragile items included in a new online exhibition. ( ABC News: Rebecca Carmody )

"The thing that's most surprising about this document are the last words he wrote … about his work and getting the job completed," he said.

"I think that reflects the nature of the man and how committed he was to the public service and his projects.

"He was just an incredible figure of our history."

Precious treasures go on virtual display

CY O'Connor's letter and other material relating to his engineering works are featured on a new website displaying some of WA's most significant treasures and stories for the first time.

Launched today, Culture WA is a digital portal, combining collections from the State Records Office, the WA Museum, the State Library and from next year, the Art Gallery of WA.

Culture and the Arts Minister David Templeman says the website will provide "new opportunities". ( ABC News: Rebecca Carmody )

Already, 1.6 million items — many too precious to ever be displayed — have been uploaded.

Culture and the Arts Minister David Templeman said it was essential for the state's cultural collections to be accessible online.

"It will provide so many new opportunities, whether that be to carry out family history research, find information about Australia's Aboriginal heritage, or learn more about our culture, environment and way of life," he said.

Historical WA Police records of offenders are among the items on display. ( ABC News: Rebecca Carmody )

"Being able to search across all of our extraordinary collections of objects, stories and information at the same time is more efficient and user friendly.

"It just makes sense."

Other items to be uploaded include early maps of Perth, artefacts, old police records, court documents and tabled petitions.

Among them is WA's six o'clock closing petition, tabled in 1928 during the height of the alcohol prohibition movement.

The closing petition submitted during the prohibition period called for hotels to shut at 6pm. ( ABC News: Rebecca Carmody )

Tens of thousands of Western Australians signed the document demanding hotels shut their doors at 6:00pm.

Images of WA's only full convict chain gang uniform, dating back to the 1850s, will also be uploaded.

WA's only remaining full convict uniform is stored at the WA Museum's Welshpool facility. ( ABC News: Rebecca Carmody )

It is rarely on display as the fabric is too delicate to be exposed to light, but it will have a permanent home in the new museum opening next year.

An early account of European settlement

The handwritten and illustrated diary of Mary Ann Friend, wife of Matthew Curling Friend, captain of the Wanstead, also features in the collection.

Mary Ann Friend's diary provides one of the earliest accounts of European settlement in WA. ( Supplied: State Library of WA )

They arrived at the Swan River settlement in Fremantle on the ship in 1830, having transported new settlers from Portsmouth in England.

The nearly 200-year-old diary provides one of the earliest accounts of what the colony was like, along with early interactions with WA's traditional owners, the Noongar people.

One entry reads:

"We're terribly frightened this morning. A party of Natives, 7 in number, came down to our tents. "Fortunately Matthew was at home. He shut all the females and children up in my Horse House. "I understand the Natives are quite naked with straight hair; they are black but paint their bodies red. "They pulled our breakfast about tasted everything but particularly liked the sugar."