Why is Maggie so Murky?


Dredging in Cleveland Bay. Source: MINCA.org

Hello JCU students, Townsvillians, and fellow snorkellers of the North Queensland region.

If you’re anything like me, you often look forward to escaping the city to explore our local piece of paradise on the weekends.

But sometimes, we may be disappointed that despite the weather being clear and sunny, a snorkel often isn’t possible on Magnetic Island.

I used to think that poor visibility was just the nature of all inshore reefs. But after visiting both Orpheus and Fitzroy Islands, where clear water seemed to be much easier to find, I was convinced there had to be another factor at play.

I began by looking back in time. In the 1960s, visibility on Maggie typically exceeded 10m, particularly in Arthur and Florence Bays. In fact, the reefs on the island were once equal to those found on the outer reef!

The Island’s “coastal fringes once supported coral reefs equal to any found on the Reef proper”

—Theo Brown (1972).

Today, visibility on Maggie rarely exceeds 2m

After some investigation, I found that the answer was glaringly clear. The shipping channel expanded from the early 1970s onwards, and the port obtained authority to dump dredge material at a new site, just east of the Island.

Answer: Dredge sludge from the Townsville Port is placed right next door to our local reefs

More recently, expansion of this shipping channel involves performing maintenance dredging for 4-5 weeks per year to provide greater access to the port, particularly for larger vessels.

The blue line in the graphic below shows the dredged channel, and the Dredge Material Placement Area (DMPA) shows where the majority of maintenance dredge is dumped, just 4km East of the pristine reefs of Magnetic Island!

Source: Port of Townsville

Unfortunately, winds direction in Cleveland Bay predominantly come from a south-easterly direction. When the wind stirs up sediment, silt pollution from the dredge is blown into the bays of Magnetic island, destroying the visibility for local divers and holidayers alike.

In fact, prior to any significant dredging of the channel, the Queensland Department of the Environment established a popular reef trail in Geoffrey bay. This was used as a recreational and educational attraction, where visitors could walk along the reef flat with a map, finding a diverse range of species, including branching and brain corals.

Today, the walking trail has been long abandoned, and the intertidal reef is covered in a layer of mud. Whatever the complex reasons for these declines, near-shore fringing reefs and seagrass beds along the Queensland coast are fast disappearing, and they can ill-afford further cumulative impacts from unprecedented dredging programs.

—Professor Terry Hughes, Director of the ARC Centre of Excellence for Coral Reef Studies (2014).

Source: MINCA.org

This port was designed under the Sustainable Ports Development

Act 2015. But if the maintenance dredge is continuously dumped just next door to our Island, with known devastating effects, then how is this practice sustainable? There is nothing sustainable about the annual smothering of our natural inshore reefs!

There are no plans to stop dumping dredge in the sea.

The Townsville Port have a long-term maintenance dredging plan in place, where they hope to continue dumping their dredge in the same place. Dredging has been found to decrease light levels and decrease coral calcification (growth) by up to 33% (Bak 1978).

While other ports around Australia have decreased their amount of dredging, the Townsville Port plans to increase their dredging over the next 10 years. The Port is expecting to dredge approximately 6,050,000m³ from 1 January 2019 to 1 January 2029 and dump a majority of this sediment in Cleveland Bay. See the 10-year plan below:

Source: Port of Townsville

The port gets special treatment.

Even more frightening, is that the Townsville Port and shipping channel are somehow exempt from being a part of the Great Barrier Reef Marine Park. Below, we can see an imaginary boundary which has been drawn as an “exclusion area” from the World Heritage Site, despite being located just 1km from Bremner Point on Magnetic Island.

This means that the port is somehow “excluded” from being protected under the Great Barrier Reef World Heritage Area that surrounds it.

The marine life in this region of the shipping channel are totally disregarded from any protection awarded to the Great Barrier Reef, our World Heritage Listed site.

Source: www.townsvilleport.com.au

On their website, the Port of Townsville can therefore say that the dredging “Has no direct impact in the Great Barrier Reef Marine Park General Use Zone.”

But unfortunately, the circulatory nature of the ocean does not quite work like that. We cannot simply build a fence, or draw a line and remove protection from parts of the ocean without expecting there to be nearby repercussions.

Dredge silt being dumped in this site is then blown straight towards the island where it settles in the pristine reefs of Geoffrey, Arthur and Florence Bay.

Further, the marine life in this site are totally disregarded from any protection awarded to the Great Barrier Reef, our World Heritage Listed site. Cleveland Bay is home to a plethora of marine plants, animals and birds. Many species reside here, including Snubfin Dolphins, humpback dolphins, turtles and dugongs.

Dredging poses a danger to our native and endemic species.

The Snubfin Dolphin is Australia’s only endemic dolphin. Unfortunately, there is believed to be only thousands of them remaining, and they are listed as Vulnerable by the IUCN Endangered Species list.

Australia’s Snubfin Dolphin: Source: MINCA.org

The only reliable local estimate of population size of Australian Snubfin Dolphins is for Cleveland Bay, north-east Queensland, where a population of less than a 100 individuals inhabits this area (Parra et al. 2002; Australian government, 2020).

Continuous dredging will further desamate the habitat of these dolphins, having disastrous results for the species.

A report funded by the Townsville Port Authority stated that:

“The dumping of very large quantities of dredged sediment in the early and mid 1970s probably played a significant part in more widespread changes to the seagrass beds throughout the Cleveland Bay area” (Pringle 1989, pg 74).

But the report also said we should continue to monitor these effects.

This is outrageous. Seagrass habitats are vital for the survival of not only Snubfin dolphins, but also dugongs and turtles, both which have been observed in Cleveland Bay.

Green Sea Turtle at Arthur Bay: by Tiffany Dun

Why are we letting the port “Continue to monitor” these effects on our endangered species? We know the effect of habitat loss will be detrimental, do we really need further studies to show this?

How can we expect to save the planet if we can’t even protect the local reefs in our back pockets?

Since the 1883 Townsville Port have been dredging a shipping channel in the harbour. Prior dredge was dumped in Middle Reef near Cockle Bay, creating the wasteland we see today.

A solution to this issue would be to simply relocate the DMPA site further offshore where it would not be blown onto our local reefs.

But instead of coming up with a solution, the Port of Townsville fund projects such as the MOUA, which will set up a snorkel trail on the island that is pointless if the visibility is continually ruined by the dredge.

It is time we unite and stand up to protect our island home!

What can we do?

Write to our Environmental minister:

I have drafted up a letter which you can send to our Environmental Minister, Meaghan Scanlon MP. She must reply to every letter. You can copy and paste the template below and submit concerns online here:

Dear Meaghan Scanlon,

I wish to formally submit my opposition to the placement of the DMPA site by the Port of Townsville, just 4km east of Magnetic Island.

In particular, I am concerned about the dredge spoil and its effect on our local reefs on Magnetic Island.

I believe that the objectives and purpose of the marine park, which is to protect and conserve the reef, are not being met as annual dredging continues to smother the corals and their inhabitants each year.

My main concerns are:

– Talk about your main concerns here: ie. visibility, tourism, ethics, turtles, dugongs, etc.

I believe that this issue can be easily resolved by the relocation of the DMPA further offshore.


Your name.

You can also send the same letter via email to GBRMPA (assessments@gbrmpa.gov.au) and the Port of Townsville (community@townsvilleport.com.au). (This is less likely to have an impact, but still worth a shot, am I right?)

Students: Be wary of who you work or intern for and who they are affiliated with. Do your research to see who funds your professor’s projects!

Let’s not let large industries smother our beloved local reefs right in front of our noses.

I don’t know about you, but I want my children to be able to snorkel in some clear water here on Magnetic Island.

Further Reading:

Environmental and Social Values Surrounding the Port of Townsville

Port of Townsville Limited Long‐Term Maintenance Dredging Management Plan

Port of Townsville Seagrass Monitoring Program

Maintenance Dredging Fact Sheet

Tiani Dun
Master of Science (Marine Biology) | Archive

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