Biodiversity Strategy - Gosford City Council - NSW Government

northeast lies the suburb of North Avoca whilst the town of Avoca Beach is found in the south
and southeast of the catchment.
The lake is roughly star-shaped, comprising four irregular arms and has a considerable area of
wetlands around its perimeter. Bareena Island is approximately the centre of the lake. The main
tributary to the lagoon is Saltwater Creek that enters the lagoon on the western side and drains
an area of 6.7 square kilometres, almost 60% of the catchment. Other tributaries all have
catchment areas of less than 1 square kilometre and enter the lagoon via the other arms.
High nutrient loads to Avoca Lagoon result in an annual spring outbreak of filamentous algae
that form large mats that anchor to the shallow substratum. The algal mats are made up of a
few species of filamentous algae, mostly Enteromorpha intestinalis and Chaetomorpha linum.
The mats impact on the aesthetic appeal of the lagoon but they are also an environmental
concern:
Cockrone
• the mats block sunlight and prevent the growth of seagrasses and other vegetation;
• when they die bacteria feeding on them strip the water of oxygen resulting in the
deaths of native fauna;
• they limit the production of dyanoflagellates that would otherwise absorb nitrogen
from the water and release it as nitrogen gas at the sediment water interface when
they die (this process is believed to be the major pathway for nitrogen removal in
coastal lagoons);
• the mats act as a nutrient sink, trapping nutrients in the system and causing them to
continuously cycle without release;
• the rotting mats form anoxic sludge which limits colonisation by bio-turbacious
infauna; and
• the mats reduce wind-induced circulation currents that would limit stratification of the
lagoon.
Cockrone Lagoon has the highest water quality of Gosford's ICOLLs. However, this lagoon also
suffers from macro algal blooms during Spring and early Summer. The vast majority of the
catchment is undeveloped rural land, predominantly forest with farms on the lower slopes. On
the north east side of the lagoon lies part of the suburb of Copacabana, whilst about half of the
suburb of MacMasters Beach lies within the south east part of the catchment. Beyond
MacMasters Beach the catchment adjoins Bouddi National park, separated by The Scenic
Drive.
The main tributary, known as Cockrone Creek, enters the lagoon on the western side and
drains an area of 4.2 square kilometres which is almost 60% of the catchment. Several other
tributaries including Merchants Creek to the north, have catchment areas between 0.25 and
0.65 square kilometres, and drain the remainder of the catchment.
The lagoon is an attractive feature in the local area and of environmental significance because
of the natural/semi-rural nature of much of the catchment (Figure 6.10). At present no
commercial tourist operators use the lagoon and it is generally not used for swimming except
near the entrance. There are no known references to any significant dredging or land infilling
activities within the lagoon.
Biodiversity - Technical Report Page 144