ABOUT ICOLLs
WHAT IS AN ICOLL?
Many coastal lakes and lagoons alternate between being open or closed to the ocean. These are known as Intermittently Closed and Open Lakes and Lagoons (ICOLLs). About 70 of the coastal lakes and lagoons in NSW are ICOLLs, making up 21% of all global ICOLLs.
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They are a common ecosystem, often located close to coastal towns and cities but, even though people interact with them every day, they are often misunderstood by these local communities.
WHY ARE THEY
IMPORTANT?
ICOLLs are highly important, providing nurseries and foraging grounds to a wide range of fish and invertebrates, home to a diversity of bird life, protection from storms, as well as being 'blue' carbon systems that sequester and store carbon dioxide, acting as a natural climate change mitigation mechanism. Additionally, the ICOLLs in the Byron Shire have immense deep cultural significance to the Arakwal people.
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Due to being considered “globally rare”, there is very limited knowledge on these systems, leading to much uncertainty on the future health of the Byron and NSW coastal environment. ICOLLs provide high biodiversity, high aesthetic value, significant economic value in terms of tourism and fisheries and sequester and store carbon dioxide, therefore acting as a natural mitigation measure to climate change.
​A more thorough and holistic understanding of our ICOLLs and coastal environment is essential in navigating and protecting our coasts as a community. Estuaries are some of the most threatened habitats on Earth due to increasing urbanisation, agriculture, and overall declining water quality. ICOLLs, in particular, are especially fragile to disturbances due to their limited flushing and shorter residence times, making them the estuary type most susceptible to climatic, environmental, and anthropogenic stressors.
HOW ICOLLS WORK.
Unlike most estuaries, ICOLLs don’t just flow to the ocean, instead a sand berm builds up at their entrance and closes them to the ocean – in some places for years. Some ICOLLs naturally open more often than others and some will rarely open at all. Usually, it is the amount of rainfall in the catchment area that determines how often and when an ICOLL will open. ICOLLs tend to close when there has been no rain for a long time as there is not enough of a freshwater inflow from upstream to push the sand away, so the sand berm can build up faster and the ICOLL will then close.
They are dynamic places, with the interchange of sand and waves at the ocean side and freshwater coming through the system, which can wash that sand away. These processes create an irregular cycle of ICOLLs opening and closing. ICOLLs that have more water flowing from upstream are likely to be open more often, while ICOLLs with only small freshwater flows tend to be closed more often.
ICOLLs open during wet periods where the sudden increase of water causes the ICOLL to overtop the sand berm. The water will then quickly cause the berm to collapse and scour a channel through to the ocean. After the water level in the ICOLL drops, wave action begins to create a new sand berm and the cycle is repeated.
BYRON'S ICOLLS.
In Byron Bay there are two ICOLLs, Belongil Creek and Tallow Creek, which fluctuate between being open and closed to sea waters. These sites are visited extensively by residents and the 2.2 million tourists that come to Byron annually.
ICOLLs are especially sensitive and susceptible to disturbances and face increasing pressure due to stresses caused by urbanisation, visitation of people and dogs, upstream agriculture and development, declining water quality, bushfires and climate change. ICOLLs are predicted to be the estuary type most impacted by global climate change effects.
There is a paucity of formal knowledge of these systems, and whilst local indigenous knowledge holds some of the keys to better management, there is no forum for sharing this knowledge more widely. Increased understanding is needed to determine to best way to maintain and manage ICOLL health for better fish habitat – the ICOLLs are both part of Cape Byron Marine Park – and terrestrial habitat such as birds and macro-invertebrates, and climate change mitigation and ‘blue’ carbon sequestration.
