There are four coastal lagoons (or estuaries) along the Warringah coast, all of which open and close naturally depending on rainfall and ocean conditions. Narrabeen Lagoon is jointly managed with Pittwater Council and Manly Lagoon is jointly managed with Manly Council. Dee Why and Curl Curl Lagoons are managed solely by Warringah Council.
All four lagoons are home to a wide variety of plants and animals which are especially adapted to cope with a mix of freshwater and saltwater conditions. Too much of either freshwater or ocean water can damage the system. We try to maintain this delicate balance which is complicated by stormwater pollution and unauthorised lagoon openings.
We undertake ecological monitoring on our four main lagoons which assesses 'chlorophyll a' and turbidity as a measure of its ecological condition. An annual report card is produced which allocates a condition ranking for the lagoons based on the results of the monitoring year (Nov/April) and is comparable to other NSW lagoons. The results of the monitoring program are available at the link on this page.
Stormwater is the rainwater that runs off hard surfaces such as roads, footpaths and carparks into our stormwater drains, creeks, estuaries and coastal lagoons and finally to the ocean.
Pollutants get into the stormwater through activities such as putting chemicals down the drain, using herbicides, pesticides and fertilisers in the garden, sweeping leaves down the drain, washing the car on the driveway and using chemical products around the home. The result is poor water quality in our waterways which impacts on our aquatic plants and animals, as well as our recreational use of creeks, lagoons and beaches.
Each morning, the Office of Environment and Heritage (OEH) predicts the likelihood of stormwater pollution at Sydney beaches. See today's prediction via the OEH Beachwatch link.
Urban development has increased the area of hard surfaces in our catchments. Hard surfaces don’t absorb rainfall like soil and plants do, which creates more runoff into our lagoons. This runoff, and the presence of houses close to the lagoons, can create a risk of localised flooding.
We manage this small-scale flooding by opening the entrances to the lagoons periodically to alleviate the problem. While this is at times necessary we, together with the NSW Department of Natural Resources and the NSW Department of Primary Industries (Fisheries), try to allow the lagoons to open naturally as much as possible.
Lagoons are sometimes opened to reduce the risk and severity of flooding or to improve water quality in the lagoon. The entrance to Narrabeen Lagoon is opened approximately every four years. In 2011, around 35,000 cubic metres of sand was removed from the entrance and used to replenish Collaroy-Narrabeen beach, which is prone to erosion.
Unauthorised Lagoon Openings
It is both illegal and dangerous for members of the public to open any of the lagoons. The water flowing out of the lagoon can develop into a ‘standing wave’, which is particularly dangerous because water pushing downwards can trap even strong swimmers by the pressure of the water.
It is also risky to open lagoons because the water in the lagoons is polluted by stormwater after it rains and can be dangerous to your health. It may also result in fish being killed. Each person participating in an unauthorised opening of a lagoon could be fined up to $1,100.