The Torrens Basin extends from Mount Pleasant in the Mount Lofty Ranges to West Beach on the Adelaide Plains and contains the River Torrens and the rural and urban First to Fifth creeks. Much of metropolitan Adelaide and the central Adelaide Hills lies within the Torrens Basin, an area of just over 620 square kilometres (check area).  The Torrens Basin is home for close to 500,000 people living in more than 150,000 residences.

The urban Torrens Basin, comprises the Lower Torrens (including first to fifth creeks) Catchment, Lower Little Para Catchment, Port Adelaide, Patawalonga Basin and Dry and Cobbler Creeks. Approximately 18,000 commercial and industrial premises (including most of Adelaide's CBD) are also located in this part of the basin, which represents a major proportion of Adelaide's economic and business activity.

The River Torrens downstream of the Gorge Weir, flows south-west out of Highbury, past Walkerville, into the City of Adelaide and the Torrens Lake, then past Thebarton, and out to the coast at West Beach. Across the Adelaide Plains, the River Torrens and its tributaries have been highly modified from their natural state. In the Port Adelaide area a series of small urban subcatchments discharge to the Port Adelaide River estuary system directly through West Lakes or Barker Inlet, the Range or Magazine Creek Wetlands to Barker Inlet and Port Estuary. The Little Para River, downstream of the Little Para Reservoir, flows westerly across the Adelaide Plains through Salisbury into Barker Inlet. Barker Inlet is one of South Australia’s largest estuaries, providing an important habitat for mangroves, seagrasses, birds and fish, and is an important nursery area for various fish and crustacean species. The lower reaches of the Little Para River have been extensively affected by urban stormwater runoff, as well as grazing land use with fertilisers and animal waste washing into the river.

Regional stormwater (capture from the upper catchment and the Adelaide plains) is considered an asset, and is being used to supplement traditional water resources.  Significant re-use projects are occurring including the irrigation of parklands, reserves and ovals within the basin.

Glenelg to Adelaide Park Lands Recycled Water Project has the capacity to provide more than 3.8 billion litres of high quality recycled water annually. In addition to supplying existing customers, the project will provide a minimum of 1.3 billion litres each year to irrigate the Adelaide Park Lands. The project provides a sustainable long-term solution for watering the Park Lands and can provide opportunities for the development of additional recycled water initiatives. It will contribute to a range of significant environmental benefits including:

• Reduced discharges of treated wastewater to the Gulf St Vincent
• Increasing the annual reuse of treated wastewater from the Glenelg Wastewater Treatment Plant by more than three times
• Improved health of the River Torrens and quality of the water in Torrens Lake

Across the basin wetlands are being used to treat urban stormwater prior to release into estuaries and the marine environment.  Barker Inlet wetlands, are a constructed series of wetland ponds, and are a combination of both freshwater and tidal environments. The Barker Inlet wetlands span 172 hectares and are fed by four stormwater drainage systems, carrying urban and industrial stormwater runoff from a catchment of approximately 4500 hectares, extending as far as North Adelaide. A primary function of the Barker Inlet wetlands is the improvement of the quality of water discharging into Barker Inlet. Water quality monitoring at the outlet has shown that the wetlands are fulfilling this function.

The Patawalonga Lake is man-made and 1.6 km in length. The lake runs parallel to the coastline from Glenelg to West Beach in Adelaide. To ensure the lake is kept clean and healthy and to avoid flooding in the area, a seawater circulation and stormwater outlet system was designed. This system diverts stormwater to the sea and allows seawater in to flush the lake on the rise and fall of the tide.  Stormwater from surrounding areas is prevented from entering the Patawalonga Lake and flows directly to sea via the Barcoo Outlet, which is buried pipe that extends 200 metres out to sea. Occasionally high flows of stormwater may be permitted to enter the lake for later discharge to the sea.

Media and community concern over the state of the River Torrens, specifically the Torrens Lake’s susceptibility to cyanobacterial blooms over the summer of 2005 / 2006 led to the establishment of the Torrens Taskforce in September 2006 to review the situation. The recommendations of the Taskforce contained in the Torrens Taskforce Summary Report of May 2007 can be categorised into three groups, namely:

1. Setting of specific water quality objectives and reviewing and upgrading monitoring to regularly measure progress in achieving these objectives.
2. Actions to be accelerated from the current management programs (e.g. fencing off watercourses to stock and expanding the gross pollutant trap (GPT) facilities to cover all significant stormwater discharges, including First Creek which discharges near the Botanic Gardens).
3. Undertaking a range of strategies in order to meet the necessary water quality targets set for the Torrens Lake (and, thereby, to avoid cyanobacterial blooms).

Actions were further prioritised in 2009 and update report developed by the Board. 

Pollution in coastal waters may put recreational users at risk, particularly swimmers. This could result in beach closures for public safety. However, pollution of coastal waters more commonly reduces the attractiveness of the water, can cause algal blooms and fish kills and has been found by the Adelaide Coastal Waters Study (ACWS) to contribute to the loss of seagrass. Discharges into the Adelaide coastal waters from waste water treatment plants, industry and stormwater outlets are high in nutrients and suspended solids. Excess nutrients cause algal blooms and epiphyte growth on seagrass leading to loss of seagrass. Discharges of high levels of suspended solids into the Adelaide coastal waters increase turbidity levels contributing to poor recreational water quality and may result in beach closures. The formal study results are not finalised, but it is understood that stormwater nutrients, turbidity and sediments may have been a contributing factor to seagrass die-off. Stormwater is the major contributor (67%) to sediment load discharged into the coastal environment. The Torrens River discharges some 10% of the total annual suspended solid load estimated at about 6600 tonnes. In contrast, wastewater treatment plants discharge some 71% of the total nitrogen load, the nutrient which is believed to have been a major cause of large-scale losses.

Implementation of some of the recommendations from the ACWS will come under the Adelaide Coastal Water Quality Improvement Plan (ACWQIP) - an initiative led by the SA EPA with funding support from the Australian Government Coastal Catchment Initiative - being developed in 2008. The ACWQIP will include the targets set for the Port Waterways in the Port River Water Quality Improvement Plan and Appendices.

The EPA has completed a risk assessment for the Gulf of St. Vincent.  Within this region the EPA identified 156 threats to water quality assessed for the eastern sector of the Gulf (the area between the Gawler River and Sellicks Beach extending approximately halfway across the Gulf), 5% of all risks were considered to be high. These threats to environmental values are the impact of nutrients and turbidity throughout the region. This risk is primarily from nutrients from the SA Water wastewater treatment plants (WWTPs) and turbidity from urban stormwater, ammonia from Penrice Soda Products and elevated temperature from the AGL Torrens Island Power Station.

The Heathfield Wastewater Treatment Plant discharges into the Sturt River. This discharge impacts on the natural flow pattern of the river by providing significant base flows throughout the year. Watercourse monitoring undertaken in 1994-95 indicated that the upper Sturt Creek (upstream of the concrete lined drain and through Hawthorndene) was one of the healthiest streams in the Mt Lofty Ranges catchment area. SA Water completed upgrading the WWTP in mid 2004 which has dramatically reduced down to very low levels the nutrient load released to the stream.

Monitoring macro invertebrates offers a good insight into the health of waterways because the number, species and diversity of macroinvertebrates is influenced by water quality, flow regime, sediment and habitat conditions in the river. The assessment of river health based on macroinvertebrate data has been standardised under the Ausrivas scoring system. First Creek above the waterfall is the least disturbed sub catchment of the River Torrens with much of the catchment contained within the Cleland Conservation Park. As a consequence water is very good quality and flows all year round. Habitat is also in very good condition.

A large investment has been made during the last ten years in the installation of gross pollutant traps (GPTs). GPTs collect litter and debris and prevent it from entering the river. A significant proportion of what is collected is sediment and organic material. An assessment of the stormwater outlets into the river shows that there are about 220 outlets between the beach and the Gorge. Of these, 48 are equipped with a GPT. The catchment served by these 48 outlets represents about 62% of the total catchment of the Torrens downstream of the Gorge.