The Fleurieu Coastal Basin comprises a group of smaller catchments on the Fleurieu Peninsula and covers 984 km². It is located approximately 75 km south of Adelaide, encompassing the areas of Carrickalinga in the North to Cape Jervis in the South and across to Port Elliot and Hindmarsh Tiers.

The average annual rainfall in the Catchment is 750 mm, varying between 500 mm at Carrickalinga and 900 mm in the central sub-catchments. The major streams include the Yankalilla, Inman and Hindmarsh rivers and Deep Creek. The Catchment disperses water from the central plateau to Gulf St Vincent to the north and Encounter Bay to the south. The Catchment also supports many wetlands that are listed as critically endangered ecological communities under the Commonwealth Environment Protection and Biodiversity Conservation Act 1999.

The wetlands of the Fleurieu Peninsula support many species of plants and animals of high conservation significance. These include 742 plant species, of which 139 have conservation status, including 73 species having status under the State National Parks and Wildlife Act 1972 (NPW Act), and 6 species being listed as threatened species (3 are listed as endangered and the other 3 are listed as vulnerable) under the EPBC Act. The wetlands of the Fleurieu Peninsula have also been recorded as supporting 183 vertebrate species. Of these, 22 species have conservation status under the NPW Act, and 3 species are protected under the EPBC Act.  The provision of environmental flows of sufficient quality and quantity is contained within the draft Water Allocation Plan for the Western Mount Lofty Ranges.  The catchments of the Fleurieu do not contain any major reservoirs., but environmental flows in the region are impacted by farm dams. In 1999 there were 5460 farm dams, which increased to 5900 in 2005.  Irrigated pasture has been, and continues to be, the most common type of irrigated agriculture. Irrigated grapevines have also emerged as a significant use of irrigated land. The total irrigated area in this region has increased substantially prior to 2000 but has not changed significantly since.

The major land use in the Fleurieu is agriculture (60.3%), the majority of which is livestock grazing. Rural residential (24.5%) is the second highest land use in the area, and occupies the eastern half of the area, between Myponga and Middleton–Victor Harbor. A change in use from rural residential to residential, showing denser housing has been noticeable in the Fleurieu, which has shown large population growth over this time.  The growth in population places pressures on water resources from a demand and waste management perspective.

The EPA has assessed River Health in the Fleurieu Peninsula, stating that “the region is biologically highly diverse, with over 350 types of aquatic macroinvertebrates having been collected from 1994–1999. Most sites are in good condition and similar to other reference rivers in the State. This is not surprising given the wet climate, high amount of vegetation cover on the landscape, and less severe land use impacts in this region compared to more urban areas. Biodiverse sites were located in the Carrickalinga area and in the Inman River catchment. The sites that were below reference condition included the Inman River downstream from treatment plant discharge, Myponga River downstream from the reservoir

The Victor Harbor wastewater treatment plant was commissioned in 2005. The new facility treats wastewater to a standard suitable for a wide range of reuse options including irrigation of farmlands, parks and gardens. Hindmarsh Valley reservoir (taken out of water supply service) stores treated wastewater for reuse and ensures managed discharge of treated wastewater into the Inman River. A reduction of the nutrient content in the treated wastewater decreases the impact on the river and Encounter Bay's marine environment. Unfortunately the nutrient rich sediments from the old treatment plant may cause water quality concerns in the Lower Inman for many more years.  SA Water and the City of Victor Harbor are developing a master plan for recycled water to be used for city irrigation.

The Inman River has had significant environmental improvements in the last 13 years, with a particular interest and expertise in water quality management, riparian restoration, protection of remnant vegetation and revegetation. Since the development of a Watercourse Management Plan in 1995 extensive on ground works have been undertaken including;

• Over 100 km of stock exclusion fencing completed
• More than 40,000 local native trees and shrubs planted
• Approximately 50ha successfully direct seeded with local native plants
• Many hectares of woody weeds controlled and
• Stabilisation of many areas prone to erosion.

Water quality issues can result from point sources (such as the historic discharge from the Victor Harbour wastewater treatment plant) or diffuse sources (such as gully or watercourse erosion which mainly occurs in association with the unstable glacial soils of the region, or agricultural practices (such as animals grazing in watercourses or the in appropriate application of fertilisers).  Surface water quality throughout the basin is highly variable both temporally (through time) and spatially (from place to place). Pollution loads are largely influenced by rainfall events, with large rainfall events contributing the majority of pollutant exports.