A new project to install an artificial reef alongside the Sydney Opera House will hopefully revitalise marine life in the harbour and restore natural habitats.
The three-year research project — a collaboration between the Opera House, the University of Technology Sydney (UTS) and the University of Sydney — intends to hang nine hexagonal-shaped modules around Bennelong Point.
It is hoped the artificial reef structures will boost biodiversity and provide a refuge for fish and other marine creatures.
"Sydney Harbour has a huge proportion of built environment, or sea walls, going all around the harbour," lead researcher and UTS professor of marine ecology David Booth said.
"These have been around for well over a century in many cases and they are made of lovely sandstone, but they just don't offer the habitat that was probably there in the first place.
"The goal is to see if we can enhance those walls to see if we can get the fish back."
What's the state of the harbour now?
More than 50 per cent of Sydney Harbour is lined by sea walls.
Professor Booth is concentrating on bringing fish back into the harbour around Bennelong Point such as baby blue gropers and sea horses.
Other projects across the harbour have had success in rejuvenating marine life, such as using old oyster shells to restore shellfish populations or transplanting seagrass to support lobsters and abalone.
"It's certainly not in horrible shape at the moment, there are quite a number of species, but that doesn't mean they are doing well," Professor Booth said.
"Habitats are limited ... a large dockland area or sea wall where there used to be mangroves, there aren't many [fish] left."
Opera House environmental sustainability manager Emma Bombonato said the project would allow the iconic site to better connect with the environment.
"In designing the Opera House, Jorn Utzon was strongly influenced and inspired by nature," she said.
"Projects such as this enable us to continue that legacy by inspiring greater community awareness of the marine environment around Bennelong Point and contributing to local biodiversity."
Constructing the reef
Researchers will start by recording data on fish numbers and the diversity in underwater areas around the Opera House and other harbour sites before installing the reef early next year.
The modules will be fairly subtle and each will be more than a metre long with various levels of "complexity".
David Lennon, a reef designer from Melbourne who has been constructing reefs for 26 years, has been hired to work on the project.
"It's about creating productive habitats and marine life and understanding how marine life use structures, it's like making apartment blocks," he said.
"We understand marine life need different entranceways, rooms, gaps to walk and move.
"We're just like underwater architects and town planners. It's like building a city, and to have a vibrant city you need a diversity of habitats."
Mr Lennon said while the reef's final design was yet to be decided, the modules would likely be an irregular cube or sphere shape in various sizes and be made of lightweight marine concrete and fibreglass.
"Little fishies like hidey holes," Professor Booth explained.
He said he hoped the reef would be rolled out permanently if significant marine changes were recorded over the next three years.
The project is being funded through an $86,000 NSW Government restoration and rehabilitation grant with in-kind contributions from the Opera House and UTS.