The Swan Canning river system consists of 31 sub-catchments which collectively cover 2,090 square kilometres (Figure 6, Figure 7). The Swan River and the Avon River are part of the same river system, flowing 280 kilometres from Wickepin to the Indian Ocean at Fremantle. The Swan-Avon River drains a total catchment of approximately 126,000 square kilometres. Land use along the Swan and Canning Rivers is primarily urban development along the lower estuary and middle reaches, with the upper estuary and river zones also including cattle grazing, horticulture and light industry.
The Swan Canning river system runs through the heart of Perth and has been the lifeblood for both the Aboriginal people and the Europeans who settled the Swan River colony. Declared the State’s ‘first heritage icon’ in 2004, the Swan River is an important historical, economic and recreational icon for Western Australia. The Swan Canning Estuary supports a rich diversity of plants and animals including seagrasses, bottlenose dolphins, sea horse colonies, sea stars, Perth Herring and Mulloway.
Rapid population growth and increased urban development in the Swan Canning catchment has contributed to a decline in the quality and quantity of water resources over time. Nutrient flows into the Swan Canning river system have led to eutrophication, algal blooms and fish kills. A major toxic blue-green algal bloom occurred in 2000 which resulted in the unprecedented closure of the whole estuary and its rivers to fishing and recreation for twelve days. Other key threats facing the rivers include erosion and sedimentation, climate change, changes to quantity of water flowing through rivers and drains, loss or degradation of salt marshes and shoreline vegetation, non-nutrient contamination and acidification (Auditor General 2014)
The wetland systems of the Swan Coastal Plain extend across three NRM regions from Moore River in the north to Mandurah in the south. The Swan Region is home to three Ramsar wetlands: Becher Point, Forrestdale Lake and Thomsons Lake. According to the Directory of Important Wetlands in Australia, the Swan Coastal Plain Interim-Biogeographic Regions of Australia (IBRA) Region has the greatest number of nationally significant wetlands in Western Australia, with 29 sites recorded. Of those, 13 are found in the Swan Region such as Becher Point Wetlands, Booragoon Lake, Brixton Street Swamps, Ellen Brook Swamps System, Forrestdale Lake, and the Gibbs Road Swamp System. Wetlands of the Swan Coastal Plain have been heavily affected by urban and industrial development, with only 20% of the original wetlands remaining (Environmental Protection Authority 2004). Of the remainder, only 15% have retained high ecological values. Along with development pressure, the increasing use of groundwater and the significant decline in rainfall poses a major risk to the remaining wetlands.
Groundwater is an essential resource for wetlands and cave systems in the Region. The Ramsar listed Forrestdale and Thomsons Lakes are fed by the Jandakot groundwater mound and the Yanchep Caves unique stygofauna communities are reliant on water from the Gnangara mound. The Jandakot and Gnangara mounds also recharge the deeper semi-confined Leederville and Yarragadee aquifers. The abstraction of groundwater to support Perth’s growing population, along with reduced rainfall as a result of climate change, is posing a significant threat to groundwater dependent ecosystems.