A very old and musty book can sometimes seem like a biohazard, and the books on the bottom floor of the Australian National University's Chifley Library could come close.

Now that the water from Canberra's flash flooding has receded, staff have been able to get inside the university's most prestigious library to see the damage — but only after donning protective masks.

Parliamentary papers, Hansards, records from the Australian Bureau of Statistics, and dozens of history and philosophy books — some very difficult to replace — all rest in the library's basement.

And on Sunday, they were under a metre of water.

Books and journals scatter the floor between library shelves, still covered in mud from the flood. ( ABC News: Jake Evans )

When staff first descended into the flooded library, they had to wade through the flotsam of papers torn asunder, and the spines of books ripped apart by the power of the water.

"It's very distressing, it's a very sad time for us," chief librarian Roxanne Missingham said.

Staff sifted through the wreckage by torchlight as the heat and humidity built, hurrying to make it safe enough for conservators to enter.

It was an urgent salvage job; many of the articles may be the only copies in Australia.

Those that survived the floodwaters are now threatened by mould — and librarians face the powerful stench of thousands of old wet books in the race against nature to save them.

The water level line — about a metre-high — is still visible on the library's shelves. ( ABC News: Jake Evans )

"If it's an individual book that we want to recover … what we would do is seal that up, place it in [a] bag and put it in the freezer, and that stops any additional damage," Ms Missingham said.

In a sorry sight for any bookworm, many of the old books have slowly swelled on their shelves, buckling and bending the cabinets they rest on.

But the happy news is the university's national treasures — historic photographs, maps and films — are housed in another library, untouched by the rapid torrents.

"It can be rebuilt," Ms Missingham said.