Manly Lagoon is a shallow coastal lagoon 12 kilometres north-east of the Sydney Central Business District. The water body of the lagoon has a surface area of 13 hectares and extends 3 kilometres west and north from the lagoon mouth on Queenscliff beach. The lagoon has a catchment of 1800 hectares consisting of 3 sub-catchments drained by the major creeks including Burnt Bridge Creek, Manly Creek and Brookvale Creek.

Once an unspoilt coastal wetland, and only 30 years ago a swimmable waterway providing fish habitat and numerous recreational opportunities, Manly Lagoon is now 10% of its original size and is considered one of the most polluted lagoons on the east coast of Australia. Swimming, boating and fishing are banned due to polluted water and sediment.

Manly Lagoon Estuary Management Study, 1995: "The water of the lagoon is eutrophic (oxygen depleted) and sensitive to further increases in nutrient inputs ... Manly Lagoon sediment is contaminated with heavy metals and, compared with Sydney Harbour or Curl Curl Lagoon, has the highest average levels of copper and lead ... Indigenous vegetation is severely depleted... as such, any areas of remnant vegetation should be maintained and conserved as a valuable resource."

WHAT'S BEING DONE:

The Water Quality Monitoring & Rehabilitation of Manly Lagoon Catchment Project

A National Landcare Grant to the Manly Environment Centre (MEC) has funded the continued employment of a Catchment Liaison Officer (CLO) whose role is to work with the community, industry, golf courses, students and other stakeholders to enhance the Manly Lagoon Catchment.

Acting as a central point of contact, the CLO continues to be based at the MEC's Waterwatch Centre and will co-ordinate the following projects:

• WATERWATCH - Water quality monitoring lagoon & creeks

• Community education and awareness

• Lagoon clean-ups

• Golf-course best practise management plans

• Industry education programs

• Regeneration and revegetation

The open space generally lies adjacent to the lagoon and its tributaries. Approximately half of the open space is linked to Manly Dam, which ceased operating as a water supply source in 1942 and is now a recreational resource.

Source: Manly Lagoon Estuary Management Study 1995

Physical Changes

Development within the Manly area became rapid following completion of the Sydney Harbour Bridge in l932. All suitable residential areas were quickly taken up and market gardens sprang up along the creeks, which fed into the lagoon in North Manly and Brookvale.

The waterways of Manly Lagoon and its tributary creeks have been the subject of significant man-made changes over at least the past sixty years or so. Of particular interest is that Hinkler Park was an island up until the l950s when the former southern channel, some l3 to l5m wide, was artificially closed during bridge and roadworks and replaced by a small 600mm diameter pipe culvert.

Lagoon Park as far south as the present Stella Maris School

Aitken Avenue

Manly Golf Course

Hinkler Park,

Warringah Golf Course (south of Kentwell Road)

District Park (now Nolan Reserve)

Warringah Mall shopping centre

Playing fields off Aquatic Drive

Passmore Reserve

Addiscombe Road

T.S. Condamine

Wakehurst Golf Course

Addiscombe Road

Lagoon Park (eastern end)

Playing fields off Aquatic Drive

Along the southern side of the waterway from Manly Creek downstream to the eastern end of Campbell Parade

Source: Mcinnes, H. Problems and Principles in Estuarine Management

The Manly Lagoon Estuary Management Study (1995) states that:

• The water of the Lagoon is EUTROPHIC and sensitive to further increases in nutrient inputs.

• Manly Lagoon sediment is CONTAMINATED with HEAVY METALS and, compared with Sydney Harbour and Curl Curl Lagoon, has the highest average levels of copper and lead. The concentrations of heavy metals in the muddy surface sediments of the lagoon appear to have increased significantly over the period l985 to l993. On the available data, concentrations of lead, mercury and zinc exceed overseas sediment standards (Washington, USA) over much of the lagoon.

• There are 29 Sydney Water sewer overflows in the catchment.

A eutrophic lagoon has limited aesthetic appeal due to high turbidity and the potential for periodic blooms of planktonic algae, including in some instances blooms of toxic blue-green algae. "Apart from visual problems, algal blooms could generate other water quality problems such as production of unpleasant odours, deoxygenation and ultimately fish kills" (Cheng, 1993).

Weirs: on Manly Creek to water Warringah Golf Course

on Burnt Bridge Creek to water Balgowlah Golf Course

Bore: to water Manly Golf Course

Manly Dam: to water Wakehurst Golf Course

Manly Lagoon has been identified as the State's most polluted coastal lagoon. Boating, fishing, and swimming are no longer allowed and the area has now been classified as a high risk area.

The water quality results for 1992/96 by Laxton showed that:

• Dissolved oxygen levels in Manly Lagoon and the tributary creeks were very variable and often fell to ecologically dangerous levels.

• Water in Manly Lagoon was often turbid due to suspended material derived from the catchment of phytoplankton blooms.

• Nutrient levels in Manly Lagoon, Brookvale Creek and Burnt Bridge Creeks were variable and considered, on average to be too high to control the growth of excess phytoplankton and other aquatic plants.

Source: Laxton, J. Water Quality of Manly Lagoon 1992/96

The following are compliance charts that illustrate water quality of Manly Lagoon over the last 8 years.

There is little habitat for aquatic life because:

• The natural vegetation of the lagoon has been greatly modified by urban development and the spread of introduced plant species.
• There are no saltmarshes or mangroves and only very small amounts of seagrass which fringe the shoreline in the lower reaches of the lagoon.

Fish species that can be found are:

• Mullet
• Bream
• Flathead
• Whiting

Tropical fish species that have been found in the Lagoon are:

• Mangrove Jack
• Giant Herring
• Big-eyed Trevally
• Australian Bass

In the creeks above Manly Dam, there is a Gondwanan fish species called Galaxias Brevipinnis, commonly called the Climbing Galaxias. This Gondwanan fish, which lives in Curl Curl creek is also found in New Zealand, another fragment of the great southern continent Gondwana. This fish is reputed to be the first fish to conquer the New Zealand Glacial lakes because of its phenonmenal climbing ability. It is a threatened species in Manly Dam.

The diversity and abundance of these is relatively low and particularly poor in the middle and upstream locations of the lagoon. This is indicative of poor bottom water quality and sediment contamination.

The Red-Crowned Toadlet (Pseudophryne australis) is restricted to Hawkebury Sandstone areas in the Manly Dam area. It is also a threatened species.

The indigenous vegetation communities originally associated with Manly lagoon and its tributaries have been heavily altered by urban development. There has been widespread introduction of ornamental exotic species such as Coral Trees which seasonally contribute very substantial amounts of leaf matter into the tributaries and the lagoon to the detriment of water quality. Weed infestations are common throughout the study area, particularly where maintenance is less intensive, detracting from the water quality, habitat value and recreational amenity of the waterways.

A recent Survey of the Vegetation around Manly Lagoon found that:

Endangered plant species: Tetratecha grandulosa (community of endangered Duffy's forest vegetation) found at the top of the catchment