A team of specially trained engineers will dive inside the Haweswater Aqueduct to examine the state of the 90km-long structure.
Prior to the commencement of the adventurous work, the United Utilities, operating the 1930s water pipe, has temporarily emptied the aqueduct to enable the engineers to get in.
The 80 engineers who will carry out the inspection have all undergone tough fitness and psychological tests to make sure they will be able to work in such a challenging environment.
"The depths, confined spaces and pipe deposits will make it like another planet down there, which is why we need to be confident they are up to the task,” said Carl Sanders, senior project manager at United Utilities.
"Also, with some sections of the pipe 19km long and hundreds of feet below ground level, ensuring the safety and wellbeing – both mental and physical – of our crews that enter the aqueduct is vital,” he said, explaining the team would have to be prepared to work in the dark, walk on an extremely slippery surface, and collect structural data at the same time.
To help the project, 16 specialist Vehicle Access Systems, known as pipe-mobiles, designed and built in Canada have been flown over to help transport equipment and supplies inside the aqueduct.
United Utilities has spent £22m in the past 10 years, planning the detailed structural analysis.
"It's a once in a career lifetime opportunity to be involved in a structural analysis of this scale and on a piece of engineering legacy,” said Sarah Togher, an engineer with United Utilities.
"It's challenging but exciting to be involved in a project that will be a part of history in itself."
The Haweswater Aqueduct brings 570 million litres of water each day from Haweswater Reservoir in Cumbria to Heaton Park reservoir, supplying two million people in Manchester and surrounding villages.
The two-week survey will help plan future maintenance work on the aqueduct to keep it flowing for years to come.