A catchment is an area of land where water collects when it rains. As the water flows over the landscape it finds its way into streams and down into the soil, eventually feeding the river. Some of this water stays underground and continues to slowly feed the river in times of low rainfall. Every inch of land on the earth forms part of a catchment. 

Catchments can vary greatly depending on the scale of management. From a dam catchment on a farm,  small sub-catchments such as Lake Matilda which feeds part of the larger Kalgan River Catchment, to the larger Oyster Harbour Catchment which spans both the Plantagenet Shire and City of Albany LGA.

The Oyster Harbour Catchment is situated along the South Coast of Western Australia and is a part of the South-West Botanical Region. It stretches from Albany through to Tenterden, across the Stirling Ranges to Chillinup, and South to, but not including, Two Peoples Bay. The entire area is approximately 3000 square kilometres and includes populated centres of the City of Albany and the townships of Mt Barker, Porongurup, and Kendenup.  There are a total of 48 sub-catchments contained within the Oyster Harbour Catchment. 
Catchments are complex and something happening in one part of the catchment can have a big impact on other parts. 

The Oyster Harbour is the centre catchment of the Albany Hinterland and shares its common borders with the Wilson Inlet Catchment to the West and Albany Eastern Hinterland to the East. These catchments fall into the South Coast Natural Resource Management Inc. area of responsibility that includes the South Coast, from Walpole in the West to Esperance in the East. In recent years the OHCG has also worked in adjoining areas of the Albany Eastern Hinterland including Manypeaks and South Stirling's. 
​
Why are catchments important? 

The idea of catchments is useful, as it is the standard functioning unit of the landscape: water, soil, plants, and animals are all linked together within a catchment through ecological processes, and any activity that occurs within a catchment will affect the whole catchment. Healthy catchments are important for human survival, as it is where our food is grown and where all the water we drink comes from.

What is a healthy catchment?

A healthy catchment is one that still has all of its ecological functions. It should be able to filter and clean water as it flows overland and seeps through the ground, and there should be lots of opportunities for water to seep into the ground so that it can be used by plants. 

What is wrong with our catchments now?
​
​Our rivers and streams are highly valued for the wide variety of social, cultural, recreational, environmental, and economic services they provide. These include water sports, fishing and marroning, nature-based recreation and ecotourism, and water supply for a range of agricultural, industrial, and urban uses. A properly functioning ecosystem supporting native biodiversity is critical to maintaining the intrinsic values of rivers and the essential services they provide. However, because of our use of rivers and the development pressures they face, aquatic ecosystems are exposed to significant and increasing stress.  Notable impacts include changes to natural flow patterns and connectivity (interrupting species migrations and flushing), poor water quality, reduced instream and fringing vegetation and habitat, and introduction of exotic species (which predate and/or compete with native species and bring disease and parasites).

The Oyster Harbour catchment has a reasonably high native biodiversity, with 15 species of native fish and crustaceans observed. This included eight species of native freshwater/freshwater-estuarine fish, the pouched lamprey, which migrates from the ocean into the headwaters of rivers to spawn, and four species of freshwater crustaceans (crayfish and shrimp). Ten of these species are endemic to the South West of Western Australia (WA), which means that these species are not naturally found anywhere else.

There are currently several pressures on the health of the river ecosystems, including:
  • Historic clearing reflecting urban, cropping, and grazing land uses in the catchments. Approximately 70 percent of vegetation in the catchment has been cleared, particularly through the stream corridor, which is having an impact on water quality and habitat. Resulting issues include:
    • Low dissolved oxygen concentrations
    • High nutrient and metal loads
    • Loss of complex in-stream shelter particularly woody habitat
    • Loss of genetic diversity in threatened wildlife 
    • Loss of landscape resilience 
  • Presence of exotic fish and crayfish species, which influence native species through competition, predation, and changes to habitat
  • Access to rivers by livestock resulting in:
    • Erosion, contributing to sedimentation
    • Loss and trampling of fringing vegetation
    • Potential water quality issues and an increase in nutrients entering the waterway.


The more stress our environmental systems face, the less they are able to tolerate and adapt to a changing climate, pressures from expanding and intensifying development, and increased frequency and magnitude of bushfires.