Boats wreak hidden havoc on the harbour. Now the damage is being undone

The thousands of yachts that dot Sydney’s bays and inlets are a sign of the harbour’s shift from working port to pleasure playground – but beneath the water is a damaging secret.

The more than 6000 boat moorings in Sydney Harbour almost all use an old-school design – a chain leading from a concrete block to a floating buoy. As the chain swings around in the swell and current, it gouges the seabed and destroys seagrass meadows that are crucial habitat for fish.

Apart from remnant industry and stormwater run-off, this is one of the biggest environmental threats to Sydney Harbour.

Now 10 environmentally friendly moorings have been installed at Balmoral Boatshed. From above the water, it looks the same and there is no functional difference for the boat owner. Beneath the surface, the concrete block has been replaced by a helical screw anchor and the chain with metal connectors and rope kept off the sea floor with several riser buoys.

On Thursday, a team of scuba divers from the Sydney Institute of Marine Science (SIMS) planted seagrass underneath the moorings for the first time.

NSW Maritime, within Transport for NSW, licenses about 21,000 moorings around the state – including 6250 in Sydney Harbour, 6770 in Hawkesbury and Broken Bay, and 2360 in Botany Bay and Port Hacking. The moorings include those owned by private individuals, commercial operators such as Balmoral Boatshed, sailing clubs and courtesy moorings that people can use for an hour or two.

“Environmentally sensitive moorings are particularly valuable in seagrass habitats, providing ecological benefits, though they require higher installation and maintenance investments,” a NSW Maritime spokesperson said.

Dr Francisco Martinez-Baena, project manager of Project Restore at SIMS, said the team planted endangered Posidonia australis – which has a natural range from about the NSW Mid North Coast to Western Australia, wrapping around the southern side of the continent.

“Posidonia is a plant that grows in the water and creates these beautiful, lush meadows that are fantastic habitat for a lot of different species, including those we like to eat like snapper and flathead, and stores huge amounts of carbon,” Martinez-Baena said.

The Posidonia fragments are collected with the help of citizen scientists when they are washed up on beaches after storms, mostly from other waterways around Sydney with more abundant seagrass. The plants are allowed to recover in tanks at the SIMS site in Chowder Bay, Mosman, before they are replanted in the wild at a density of 40 shoots per square-metre plot.

Project Restore first planted seagrass in 2024 at Cobblers Beach – a place chosen because as a Navy site, it was off limits to recreational boaters, Martinez-Baena said. It had an 80 per cent survival rate after a year. Since then, there have been plantings at Vaucluse and Watsons Bay, and similar restoration work is occurring in Botany Bay led by the Gamay Rangers. However, the planting at Balmoral was historic because of the boat moorings.

“For the first time in Sydney Harbour now, we are planting seagrass underneath moorings, which is a major success for the city,” Martinez-Baena said.

Seagrass damage was “a problem all over the planet”, he said, and the species grows slowly so areas damaged by moorings and anchors can take decades to regrow, if at all, Martinez-Baena said. Environmentally friendly moorings had been installed overseas including in Brazil, Spain and Britain and elsewhere in Australia such as Moreton Bay in Queensland.

Adriana Verges, a professor in marine ecology at UNSW and the Sydney Institute of Marine Science, said it was long and arduous process to get approvals for both the seagrass restoration and the new moorings.

“All the permit applications and all the paperwork is made for damaging nature. We’re trying to do the opposite, but the system’s not quite fit for purpose,” Verges said. ”This is not something that is unique to Australia, it’s worldwide.”

Steven Hedge, owner-operator of the Balmoral Boatshed, said he was keen to be involved and had been aware that the environmentally friendly moorings were successfully used overseas.

“We had two motivations – one was the environmental credentials that we pick up from participating in it,” Hedge said. “In addition, we gain some commercial knowledge about alternative ways to moor boats in a more environmentally sensitive way.”

Hedge would consider moving his other 46 moorings over to the environmentally friendly version, depending on economic feasibility. A traditional mooring cost several thousand dollars.

Project Restore, mainly funded by state government grants, paid for the new moorings. They cost $5000 each for the basic unit, plus an additional $7000 for the helix screw anchor that replaced the concrete block.

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