Last Chance to See the Underwater Spectacle of Lonsdale Wall

By David King, images by David Bryant

Diving the Cumberland

Diving the Cumberland

At the beginning of August, the giant dredging vessel Queen Of The Netherlands entered Port Phillip Bay to commence trial dredging at the behest of the Victorian Government.

scorted by Police and greeted by protesters on boats, canoes, kayaks and surf boards, the vessel made its way to Melbourne and the mouth of the Yarra River.

Approximately 1.7 million metres of rock, sand and silt are to be dredged from the seabed at the heads of Port Phillip Bay to test the environmental impact of what the Victorian Government has described as ‘state of the art dredging technology’.

According to David Bryant of Seapics Ltd, the approximate area to be dredged is known as Rip Bank, a treacherous site seldom dived or photographed.

But it matters little whether dredging takes place in a seldom or frequently dived area since dredging usually stirs up huge plumes of sediment which are suspended in the water and carried to other areas by tidal flow.

For those new to the story, the Victorian Government intends to dredge the shipping channels of Port Phillip Bay to allow large vessels to access the bay and the port of Melbourne. Up to 33 million cubic metres of sand, silt and rock are to be removed from areas close to ecologically diverse and fragile marine parks.

The Port of Melbourne Authority wants to conduct trial dredging to ascertain whether dredging can be carried out in an ecologically sustainable manner. Various experts, including some from the CSIRO have said it cannot be.

The Blue Wedges Coalition, which has been fighting the channel deepening proposal, is concerned that trial dredging will become ‘dredging by stealth’ and that it will be too easy for the Port of Melbourne authority to claim they might as well go ahead with the job once some damage has been done.

In the line of fire from dredging are some popular and ecologically fragile dive sites. If channel deepening goes ahead, it may well be your last chance to see …

THE UNDERWATER SPECTACLE OF LONSDALE WALL

The first time I dived this eye-popping site was in the late 1980s. I remember kneeling on a kelp-covered ledge, gazing down over a series of ledges which dropped away into the blue-grey gloom, and thinking this must have been a hill or mountain overlooking a valley back prehistoric times.

I wasn’t far wrong. Extending a kilometre into Port Phillip Bay from the Rip where ships enter, Lonsdale Wall follows the ancestral route of the Yarra River. Further to the north-east, another popular and colourful dive site known as Portsea Hole was once a depression in the bed of the river.

Today, they are simply spectacular dive sites. Lonsdale Wall drops from around 14 metres to 90 metres in a series of near-vertical rock ledges and undercuts all teeming with marine life. At 20 metres are caverns with zoanthids, sponges, soft corals and bryozoans patrolled by over 40 different species of fish including butterfly perch, long snouted boarfish, blue throated wrasse, and the iridiscent blue devil fish. Leatherjackets, sea carp, and old wives and other species of wrasse are also to be seen.

Below 30 metres are gardens of corals, jewel anemones, hydroids, and sea tulips. If it wasn’t for strict time limits on dives, it would be easy to sit narked on one of the ledges admiring this underwater garden of Eden until all one’s air and bottom time had been used up.

Strong tidal currents mean this site is only dived during slack water which lasts around 30 minutes. The currents also ensure generally good visibility – likely to suffer if dredging goes ahead on a large scale. Nearby sites such as Boarfish Reef share many of the characteristics and marine life of Lonsdale Wall and are also under threat from sediment fallout of sustained dredging.

As Blue Wedges coordinator Jenny Warfe observed ‘If (the underwater sites) were parks on land and the Government said they wanted to run a bulldozer through them, there would be a public outcry. Because it’s underwater and out of sight for a lot of people, they don’t realize what’s being done.’

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