Avoca Lagoon – Serious Environmental Stress
Avoca Lagoon is a precious jewel – providing wonderful benefits for recreation, sporting activities, and wildlife. But the regular State-wide environmental monitoring of estuaries demonstrates year-after-year that water quality (measured by turbidity) is typically poor – among the worst in NSW. Why has not yet been understood fully by scientists and Council managers.
The regular State-wide Beachwatch program measuring suitability for swimming (as indicated by presence of faecal microorganisms) in the ocean and estuaries, every year assigns a Poor grading for the Lagoon water. New scientific studies shed important light on the causes. There are several key parts to the problems, indicating the need for a comprehensive strategy to restore the Lagoon.
New Study Results – Nutrients and Turbidity
Scientists from the State Environment Department recently carried out a one year-long detailed investigation of the condition of the Lagoon water. A wide range of measurements and assessments were performed, both when the sand berm at the ocean is closed and open, and at the five main tributary streams flowing into the Lagoon. Members of a community reference group received a briefing in April; and the State scientists have just delivered a full technical report. There’s a link on our website.
The Main Basin
Historically, the whole bed of the Lagoon sat about 1 metre above sea level. And when the sand berm was open there was full flushing of the water and bottom sediment. But sand mining was permitted for a decade or so until 1994 – removing about half a million tonnes. This produced a large dredge hole in the Main Basin, affecting about 30% of the Lagoon bed area and lowering the floor there by up to almost 4 metres, dropping that part of the Lagoon below sea level.
This hole is a trap for organic material. And it is not flushed when the Lagoon is open to the sea. These organic sediments release large amounts of nutrients into the water which feeds abnormal levels of algae growth. The result is: excessive turbidity blocking penetration of sunlight; and dissolved oxygen in the bottom water layer in the hole falling to an extremely low level, unable to support fish and other life dependent on oxygen.
The South Arm – The Bridge to old Bowtell’s caravan park
The two creeks that flow into the top of the south arm (passing under The Round Drive) are the largest sources of nutrients and suspended particulates from the catchment. The bridge at the other end constricts water flowing between the south arm and the main basin. This causes sediment to become trapped in the south arm. And when wind drives wave activity in shallow water, fine particles become suspended causing turbidity.
Faecal Pollution
A 2019-20 study by the University of Technology Sydney, commissioned by the State Government and Council, examined levels of faecal pollution. Avoca Lagoon exhibited high to very high levels of faecal organisms following rainfall events. It concluded that sewage was the main source. Dog and bird faecal contamination were also significant. Council has commissioned inspection of the sewer network in Avoca Beach to determine where the mains are in poor condition and to undertake relining– 22.3km inspected and 3.3 km relined, so far. A sewer trunk main collects sewage from as far north as Forresters Beach which passes under the Lagoon to the KIncumber treatment works. A pumping station is on the northern shore near the Lagoon entrance. From time-totime the main breaks or the pumping station overflows, causing major water pollution and triggering the opening of the sand berm by Council to flush the Lagoon. Council has commenced works to install a new sewer main under the Lagoon and upgrading the shore infrastructure.
Framing an Action Plan
Our goal - a clean and healthy lagoon
Council plans to complete a new strategy – a Coast Management Program – for the Lagoon by mid-2025. Community engagement during the intervening time will be essential to frame an effective action plan to remedy the environmental problems. The Community Association will be active on that front.
Ian Carruthers