The Estuary: The lower Maribyrnong River is an ‘estuary’, which is part of the river that meets, and is affected by the sea; or Port Philip Bay in this case. The Estuary is influenced by both the salty waters of the Bay and the freshwater that flows into it.  The Maribyrnong River’s estuary is about 15 kms long. It extends from the union with the Yarra upstream all the way to Solomons Ford at Avondale Heights. Near its mouth, in the Port of Melbourne, the river is very deep, having been searched to a depth of 10 meters. Above the Port, for most of its length, the estuary generally ranges from 2-3 meters in depth.

 The Floodplain: The river in the lower Maribyrnong Valley estuary used to flood regularly reviving and nourishing associated wetlands. Since the European settlement the floodplain and the river have been substantially altered. Wetlands have been drained or filled and covered with a variety of housing and industrial sites, sporting facilities and parks. In some areas levee banks have been built to keep out floodwaters. Most of the vegetation has been cleared and the river banks have been lined with bluestone boulders. Obstacles have been removed from the water and pollution has carried on, although much reduced from earlier eras. The wetlands on the floodplain have virtually all disappeared except for several small features, all recreated in relatively recent times:-

v      Pipemakers Park:

v      Newells Paddock; and

v    Delfin/Edgewater.

 Essentially the natural environment has been simplified in ecological terms as habitats have been modified or removed, and in addition built structures and exotic vegetation have come to dominate. In spite of these changes a large variety of native wildlife can be found within the river, on its banks, in its wetland and on the surrounding floodplain and urban areas.

 A bucket of mud: To obtain information on the microscopic animals found in the Maribyrnong Rivers estuary, we employed an environmental research company, Ecowise Consultants, to carry out a study of the animals that live in the mud. This layer contains many species that live on the bacteria and algae and other even smaller creatures that live in their thousands, even millions, here and in water bodies fresh and salty. Most of the macro-invertebrates here are roughly about the size of a pinhead. All the animals you see here were basically scooped up in a bucket of mud.

Denise and Katherine from Eco-wise Consultants collect mud to be analysed in the laboratory.

 Water Quality: In the last few decades a method for measuring fresh water quality and habitat has been developed overseas and in Australia using macro-invertebrates or the small creatures that live in rivers, streams and ponds. This method, known as bio-assessment, is useful because macro-invertebrates are widespread and consistent in behaviour in their response to a variety of factors. Furthermore, it is a method that can be understood by members of the community who can also participate in the assessment. One basic principle, for example, is that water bodies with a high level of diversity are generally in good health, while in polluted habitats sensitive species are eliminated and less sensitive species show an increase in numbers. However, this system is not so well developed for estuarine and marine systems.