Toby Inlet is located 8.5km east of Dunsborough in the western half of the Geographe catchment. The Inlet is a narrow inter-barrier lagoon running parallel to the shore and separated from the ocean by high beach ridges. The Inlet is approximately 5.6 km in length and is surrounded by residential properties and holiday homes. The Inlet streams are of ecological importance, providing habitat for fish and freshwater crayfish (such as the Swan River Goby, Gilgie and the Dunsborough burrowing crayfish), waterbirds and frogs. The Inlet is also of social importance as a recreational area for residents and visiting tourists.
Land use in the catchment is comprised mostly of large rural properties in its upper catchment, with pockets of native vegetation and agricultural use. Beef grazing, urban residential properties, parks and golf courses are the primary land uses in the lower catchment.
Beef grazing and urban residential properties are the primary land-uses in the lower catchment.
The Toby Inlet catchment consists of a series of tributaries that have their headwaters in the Leeuwin-Naturaliste Ridge, and flow onto the Swan Coastal Plain where they form poorly defined channels which converge at Caves Road where they discharge to Toby Inlet. The flow of water in and out of Toby Inlet is dominated by tidal effects and flow off the catchment . Flow to the Toby Inlet has been substantially reduced through drainage modifications resulting in the natural opening of the Inlet being almost permanently closed. The mouth of the Toby Inlet naturally closes in the summer months due to longshore sand movement. The mouth is artificially opened sporadically by the City of Busselton to alleviate water quality issues. Since 2000, the mean annual flow for the Toby Inlet is 5.5GL/yr of a total of 203 GL/yr for the waterways of the Geographe catchment.
Image: Ocean Entrance to Toby Inlet
A high proportion of beef grazing occurs in the lower catchment, where fertilisers contribute to nutrient loads entering waterways. A significant proportion of nutrients (mostly nitrogen) enter the waterway through runoff from surrounding rural lifestyle properties. Septic systems also contribute to nutrient loads (mostly phosphorus) in the Toby Inlet, particularly in the summer months when tourist numbers are higher and systems are overloaded with too much wastewater in a short period of time.
Nutrients in the Toby Inlet are primarily sourced from fertiliser used for beef grazing. Septic systems and runoff from rural lifestyle properties are also a significant source of nutrients.
The Department of Water and Environmental Regulation commenced water quality monitoring of Toby Inlet in 2017. Salinity, dissolved oxygen, nutrients and phytoplankton are some of the parameters monitored fortnightly to track water quality trends over time.
Data from 2017-2021 is presented in the table below. Water quality data shows total phosphorus concentrations well below the target of 0.1mg/L. Total nitrogen concentrations are slightly above water quality targets.
The Toby Inlet catchment is categorised as an ‘intervention’ catchment as waterways are currently meeting the phosphorus target but not the nitrogen target.
Total nitrogen and total phosphorus trends for the Toby Inlet catchment from 2011 to 2021.
Since 2009 programs led by GeoCatch and partners have focussed on reducing nitrogen and phosphorus entering the waterway. These programs included working with farmers and to reduce fertiliser use, completing fencing and revegetation in the riparian zone and working with businesses to reduce nutrients and pollutants leaving their site through the Bay Friendly Business Program.
The Toby Inlet Catchment Group are a volunteer group that have been responsible for raising awareness regarding the health of the Inlet and are involved in the co-ordination and implementation of programs including beach clean-ups, water testing and stream restoration. Key achievements by GeoCatch and partners between 2009 and 2013 include:
Two grazing properties carried out soil testing and nutrient mapping to inform fertiliser decisions, assisting farmers to use only the phosphorus needed for the pasture growth required.
The Bay OK program was developed to encourage practice change by urban gardeners through workshops, seminars and demonstrations.
Three Toby Inlet businesses participated in the Bay friendly businesses program to reduce nutrients and pollutants leaving their sites.
0.315 km of riparian fencing and 5.7ha of re-vegetation was completed with the aim to protect and restore riparian vegetation, increasing the absorption of nutrients and reducing the sedimentation and pollution of Toby Inlet catchment waterways.
Management programs will continue to focus on preventing phosphorus loads rising and reducing nitrogen loads entering Toby Inlet under the Revitalising Geographe Waterways program. Implementation of best practice agricultural fertiliser management, riparian management and reducing nutrient loads from urban sources are key goals for this ‘intervention’ catchment.
The western side of Toby Inlet will be converted from deep septic to deep sewage under the Infill Sewage Program. Connections to sewage in this area are predicted to reduce nutrient loads to the Toby Inlet, reduce pathogens and improve odour. Water quality monitoring before and after the conversion will allow us to quantify environmental impacts of septic systems on this valued water resource.
The feasibility of reconnecting Toby Inlet to the ocean is being investigated using hydrodynamic modelling in the Reconnecting Toby Inlet Project. As a direct action of these investigations, the City of Busselton opened the Toby Inlet bar over summer, resulting in improvements to water quality.
GeoCatch will work with the community to support sustainable behaviours in urban areas and best management practices in fertiliser management. Monitoring the water quality of the Inlet will continue in the Catchment Water Quality Monitoring Program and the Water Quality Improvement Plan will be reviewed and updated.
Continuation of a fortnightly water quality monitoring program will track the water quality of the Inlet over time