A NSW Government website

Manly Lagoon

Our water quality monitoring program has shown Manly Lagoon to have poor water quality. Find out more about the estuary and its unique features.

Manly Lagoon is situated in the Sydney Metropolitan region of New South Wales. It is classed as a creek and has an intermittently closed entrance that meets the sea at the north end of the popular Manly–Queenscliff Beach.

Manly Dam, which was constructed in 1892, regulates the major creek that feeds into Manly Lagoon.

Water quality report card

As part of our water quality monitoring program we assess the water quality and ecosystem health of an estuary using a range of relevant indicators. We have supported Northern Beaches Council develop and carry out a monitoring program to assess the water quality of estuaries in their local government area. Sampling is carried out fortnightly between October and April each year. Three sites are sampled in Manly Lagoon.

The monitoring program has been ongoing since 2012. The most recent sampling was completed over the 2021–22 summer.

This report card represents 2 water quality indicators that we routinely measure: the amount of algae present and water clarity. Low levels of these 2 indicators equate with good water quality.

E

Algae

C

Water clarity

D

Overall grade

The report card shows the condition of the estuary was poor with:

  • algae abundance graded very poor (E)
  • water clarity graded fair (C)
  • overall estuary health graded poor (D).

Grades for algae, water clarity and overall are represented as: 

  • A – excellent 
  • B – good 
  • C – fair 
  • D – poor 
  • E – very poor.

Go to estuary report cards to find out what each grade means, read our sampling, data analysis and reporting protocols, and find out how we calculate these grades.

The past results of the monitoring program, including detailed water quality report cards, are available on the Northern Beaches Council website.

Historical water quality grades

We have monitored water quality in Manly Lagoon since 2007. This table shows the water quality grades for this estuary over that time.

YearAlgaeWater clarityOverall grade
2007-08ECD
2010-11EDD
2013-14ECD
2014-15DBC
2015-16DDD
2016-17DEE
2017-18DBC
2018-19EBC
2019-20DCD
2020-21CCC

 

Physical data

Physical characteristics

Estuary typeCreek
Latitude (ºS)–33.79
Longitude (ºE)151.29
Catchment area (km2)17.2
Estuary area (km2)0.1
Estuary volume (ML)35.6
Average depth (m)0.4

Notes: km2 = square kilometres; m = metres; ML = megalitres.

Water depth and survey data

Bathymetric and coastal topography data for this estuary are available in our data portal.

Land use

The catchment of Manly Lagoon is highly disturbed. About one-quarter of the land within the catchment remains forested. The remainder is used for urban development, including 2 golf courses.

Get involved

National and marine parks

Community involvement

  • The Manly Environment Centre, run by Northern Beaches Council, educates the community and provides opportunities for locals to get involved in coastal environmental management.
  • Northern Beaches Council also facilitates a Bushcare Program for local residents to get involved in conservation and restoration of the natural environment around Manly Lagoon estuary.
Aerial view of Manly Lagoon, showing a beachfront with waves crashing onto the shore, a river meandering through the landscape, residential areas with numerous houses, greenery, and roads, and a clear demarcation where the urban area meets the natural water bodies.

Aerial view of Manly Lagoon estuary

Local government management

Local councils manage estuaries within their area unless the estuary is attached to a marine park. Northern Beaches Council manages this estuary.

Threatened species

Estuaries provide important protected environments where native plants like seagrass and mangroves grow and create habitat for fish and other animals.

Find out more about the biodiversity in our estuaries.