Lake sludge “natural”

In recent weeks there has been proliferation of seagrasses (Zostera) in the shallow foreshore areas of Lake Illawarra.

LIA Chairman, Dog Prosser said this is another cycle in the life of the lake.

The vigorous growth of the seagrasses is caused by a combination of nutrients, water temperature, water depth and water clarity, he told the Lake Times.

Recent conditions in the lake have been ripe for seagrasses to grow.

Seagrass production tends to follow the seasonal cycle of solar radiation with maxima occurring in late spring or early summer.

At the end of the growing season (and to some extent throughout the year) much of the plant material dies and begins to decay.

Decaying seagrass wrack often results in the emission of foul odours but odours can also result from the stirring up of bottom sediments by waves whereby gases are then released through the water column into the atmosphere.

Under these conditions residents living close to the lake often complain about the health of the lake.

Mr Prosser said the only effective method of removing the excess floating seagrass wrack in shallow water was with a floating harvester.

The smallest machine costs about $10,000 a week and can only be used in small particular trouble spots.

In other areas where foreshore conditions are suitable land based machines are used, he said.

The lake has some 37 km of foreshore & the Lake Illawarra Authority simply does not have the resources for a continuous program to remove organic wrack.

On the positive side, just a few years ago during the drought years of 2002 / 2003, the level of the lake fell about 0.5m from evaporation, exposing sea grass beds to the sun, according to Mr Prosser.

The usual Authority critics of course, apart from blaming the LIA for the drought, said the seagrasses would never recover, Mr Prosser said.

Over the past couple of years, seagrasses within the lake have flourished.

As a NSW Fisheries Officer advised a community meeting in answer to a complaint about the presence of sea weeds; a coastal lake without seagrasses is a dead lake.

Seagrasses are a sign of a healthy lake.

On the negative side, Lake Illawarra, for the next twenty or thirty years, is facing the greatest threat to its existence since Bass & Flinders rowed the Tom Thumb into the entrance of the lake in 1796, according to Mr Prosser.

The growth of subdivisions in West Dapto, Calderwood, Marshall Mount, Kembla Grange & Tullimbah will introduce a further fifty to seventy five thousand people into the lakes catchment, he said.

Our challenge now is to retain the improvements the Authority has made over the past eighteen years with the assistance of the State Government and both Wollongong and Shellharbour Councils.