Narrabeen Lagoon Entrance FAQs
What is happening with the entrance of Narrabeen Lagoon?
Narrabeen Lagoon is a coastal lagoon that naturally opens and closes to the ocean depending on
how much sand has accumulated in the entrance. The entrance is kept open most of the time to
reduce risk of flooding to surrounding properties and improve water quality, however keeping the
lagoon open also lowers the water level in the lagoon which impacts on boating and other types of
recreation.
Council has two main methods of managing the entrance.
Once the lagoon has closed, Council can undertake a mechanical break out where a channel is
formed using an excavator allowing the lagoon to drain out to the ocean. In order for a break out to
be successful, the water level in the lagoon needs to be at least 1 metre higher than mean sea level
otherwise the flow in from the ocean on high tide overcomes the outflow from the lagoon and it
closes again.
Even after a successful breakout, the lagoon can close up again quite quickly, particularly if there is
still a lot of sand in the entrance (and depending on ocean and rainfall conditions). As such, this is
only a short term management option undertaken primarily for flood mitigation. This is how other
coastal lagoons on the Northern Beaches are also managed, however Dee Why and Curl Curl
Lagoons are not opened until the water level is almost 2m above mean sea level, which means they
open with a much greater amount of energy and flow, and are almost always successful. As with
Narrabeen, they stay open until the ocean sand closes them.
The second management action is entrance clearance where a large amount of sand is excavated
from the entrance area; from west of Ocean Street Bridge to the ocean, and transported back to
Collaroy-Narrabeen beach. This ensures the entrance is not constricted with sand for a number of
years and tends to keep the lagoon open (depending again on ocean and rainfall conditions). This
occurs every few years and takes a few months to complete. This is a long term management option
and requires significant planning and funding.
When will Council next mechanically break out the entrance?
Council will open the entrance when water levels are at least 1 metre above mean sea level and
there is significant rainfall occurring or forecast. Council cannot open the lagoon while water levels
are low because the flow in from the ocean on high tide overcomes the outflow from the lagoon and
it will close again. Even after a successful breakout, the lagoon can close up again quite quickly,
particularly if there is still a lot of sand in the entrance (and depending on ocean and rainfall
conditions). In November 2015, Council manually opened the lagoon at the approved water level in
accordance with Council’s procedures and the State Government Licence. Due to conditions like
wave swell, rain conditions and the amount of sand in the area, the entrance has naturally re-closed.
The water levels in the closed lagoon are largely driven by rainfall and because of this Council cannot
give an exact date when the entrance will be able to be mechanically opened again. This means it
may be closed during the summer period.
Council aims to manage the entrance in a way that balances community needs, flooding risk and the
need to maintain the natural process of a coastal lagoon (which includes periodic closure).
When will Council be doing entrance clearance?
Warringah and Pittwater Councils together with the State Government plan to do a large entrance
clearance project in winter 2016 and will remove approximately 45,000 cubic metres of sand. This
project is done around every four years and the sand is trucked down to Collaroy / Narrabeen Beach
to address erosion and improve amenity.
Predicting an entrance closure is not easy, but typically happens over a 3-4 year period. It became
clear that the entrance was likely to close towards the end of 2015 and planning for the next
clearance commenced in mid-2015. It is a complicated project with the need for multiple layers of
State and local approvals, and has to rely on up to date site conditions which makes it difficult to
undertake detailed planning well in advance of any closure. Once approvals have been obtained,
Council will seek competitive tenders to undertake the works.
Approvals are currently being prepared and the project has been planned for winter months to
minimise the impact to beach goers. Once this project is complete, the entrance will be likely to
remain open for a number of years.
Can I swim in the lagoon?
Warringah Council does not monitor water quality for swimming. Water quality at ocean beaches
and Birdwood Park is monitored by NSW Beachwatch on a weekly basis and information is published
at the web link below.
It is recommended you avoid swimming during, and at least one day after, heavy rain at ocean
beaches, and for three days at estuarine (lagoon) swimming areas. Avoid swimming if there are signs
of water pollution such as:
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Discoloured water
Fast flowing or strong smelling drains
Street litter such as drinking straws, food wrappers or leaves floating in the water or on the
tide line.
Updated information can be found on Beachwatch.
Where else can I swim?
North Narrabeen Beach is a 200m walk from the Ocean Street Bridge and the rockpool is a 500m
walk. Both may be suitable for swimming, please check conditions based on the signs of water
pollution described above.
Alternatively the Warringah Aquatic Centre at Allambie Heights has three indoor and outdoor pools
that cater to all ages.
Is Pelican Itch in the lagoon?
In Narrabeen Lagoon and other coastal waters the parasitic schistosome flat worm Austrobilharzia
terrigalensis can cause an itchy rash known as Pelican Itch, Sea Lice or Swimmers Itch. It is especially
common during summer when the water temperatures exceed 24 degrees.
The life-cycle of the flatworm is complex and involves two hosts, a bird such as a seagull and an
invertebrate water snail Batillaria australis.
When the water temperatures are warm, the parasite leaves the snail and moves to the surface of
the water seeking contact with a bird – or in some cases a human. It buries into the skin and dies
causing an itchy rash.
Pelican Itch is not an indicator of pollution. People affected by Pelican Itch should visit a chemist or
doctor for treatment.
Will my property flood?
Warringah Council Officers monitor the water level and entrance conditions through site inspections
and digital water level recorders, which are publicly available on Northern Beaches Floodwatch.
Once water levels are high enough and rain is forecast, a mechanical breakout will be undertaken in
accordance with long-standing practice (see mechanical breakout information above). In most cases
this will allow the lagoon to drain and temporarily reduce the risk of flooding. In heavy weather
conditions however, many properties may be prone to flooding even when the entrance is open
because:
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The volume of water flowing down from the catchment can be greater than what can leave
the entrance;
The amount of water washing in from heavy ocean swells and extreme tides
Some properties are very low lying