Corangamite Catchment Management Authority 64 Dennis St (PO Box 159) Colac Victoria 3250 (T) 03 5232 9100 (F) 03 5232 2759 (E) info@ccma.vic.gov.au www.ccma.vic.gov.au

The Thompson Creek Estuary is a picturesque riverine estuary which runs adjacent to the coastal township of Breamlea. It forms a part of the saltmarsh communities of the Breamlea wetlands and the important Karaaf Wetlands which are rich in local cultural history. The estuary opens to the sea at Point Impossible, but can close its mouth intermittently.

The opening and closing of the estuary mouth allows for the inundation of important saltmarsh habitats. For most of the year there is very little river flow from the headwaters to the estuary, although in some year’s floods have resulted after periods of sustained and heavy rainfall.

The Thompson Creek estuary is a popular recreation spot for fishing, canoeing and walking and is a place of cultural significance.

The mouth of the Thompson Creek estuary at a time when it is open to the sea at Point Impossible.

This brochure summarises 12 months of EstuaryWatch estuary mouth condition and physical and chemical data. Thompson Creek EstuaryWatch volunteers monitor one mouth condition site and two physical and chemical sites during each monitoring session. Monitoring was conducted in 7 out of 12 months. The Thompson Creek is an intermittently opening estuary. The estuary mouth was

recorded as being open on one occasion on May 5 2015, the estuary mouth was recorded as being closed for the remainder of the year. Estuary mouth closures were recorded at many other estuaries in Victoria during 2015, likely to be due to lower than average rainfall during 2015. Over the twelve months salinity levels indicate the estuary waters to be hypersaline (salinity greater than sea water) with no stratification evident for most of the time, the salinity ranged from 35 - 63 ppt. During August the salinity levels were the lowest for the year, being slightly greater than that of sea water. The dissolved oxygen levels ranged from 54 – 163 % saturation during the year, The high levels are likely due to the masses of algae growing in the estuary and due to the time of day that the monitoring was conducted, the lower levels were recorded when monitoring was conducted in the morning before photosynthesis by the algae supersaturated the water with oxygen. The water temperature within the estuary ranged from 7.5 °C in July to 22.4°C in February. The pH levels remained in the healthy range 7.3 – 8.6 pH units. EstuaryWatch records at Thompson Creek estuary can be viewed at www.estuarywatch.com.au.

Map of the Thompson Creek estuary including the EstuaryWatch site locations. Google Maps satellite image.

Masses of algae found growing near site T1 in the Thompson Creek estuary during times when the estuary mouth was closed.

The Thompson Creek EstuaryWatch team braving the elements at the mouth of the estuary.

– Join the Thompson Creek EstuaryWatch Group

www.estuarywatch.com.au

– Register the estuary as a clean-up site for Clean Up Australia Day

www.cleanupaustraliaday.org.au

– Join a local environment group such as the Breamlea Coast Action group, the Bellarine Catchment Network, or the Torquay Coast Action Groups

http://corangamite.landcarevic.net.au/bcn

– Share what you have learnt from this annual summary with a friend or family member.

Threats to the Thompson Creek estuary

– Livestock access upstream of the estuary

– Degraded riparian vegetation upstream of the estuary

– Altered water regime

– Invasive fauna and flora

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Type of Estuary: Riverine

Location: -38.300246,

144.374395

Nearest town: Breamlea

Estuary length: 5.5 km

River length: 48.4 km

Mouth state: Intermittently Open

Description: The Thompson Creek Estuary runs adjacent to the township of Breamlea with mostly rural properties within its catchment. It flows in a mostly south-east direction before entering Bass Strait on the eastern side of Point Impossible.

Date range: 01/01/2015 – 31/12/2015

THOMPSON CREEK ESTUARY 2015

For all four monitoring sessions chosen for the EstuaryWatch Snapshots, photo point photos and a longitudinal profile of the estuary from site T1 (Point Impossible Road Culvert at Mullet Creek ) to T2 ( Blackgate Road Pedestrian Bridge) is displayed. The profiles show the depth, salinity and percent saturation of dissolved oxygen at each monitoring site from the surface of the water column to the bottom.

EstuaryWatch members testing the water quality at site T2.

In 2015 Thompson Creek EstuaryWatch volunteers established two new monitoring sites. The Thompson Creek EstuaryWatch team have been monitoring since January 2009. When the group was established, only estuary mouth condition monitoring was conducted. This involved taking monthly photos of the estuary mouth and recording water level, wind strength, wind direction and sea state.

In response to growing interest in the health of the Thompson Creek estuary, two water quality sites were established. The first (T1) at the Point Impossible Rd culvert at Mullet Creek and the second (T2) at the Blackgate Rd pedestrian bridge. EstuaryWatch volunteers now record dissolved oxygen, temperature, salinity, turbidity and pH every month at both monitoring sites.

Common Galaxia, Galaxias maculatus

The Common Galaxias adults live in calm waters of low-elevation streams, during autumn they migrate downstream to spawn. Thousands of small eggs are laid in vegetation on the margins of estuaries at spring tides, and often spend up to two weeks out of water until the next spring tide. The larvae then leave the estuary and spend 5 to 6 months at sea as juveniles before returning to the estuary as whitebait moving upstream to the freshwater to mature.

See more at: http://australianmuseum.net.au/common-galaxias-galaxias-maculatus#sthash.tCABw6N7.dpuf

Photo: Whitebait stage Common Galaxias. Photographer: Rudie Kuiter © 0

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Average Monthly Rainfall2001-2015Monthly Rainfall 2015

Estuary Mouth Closed

Rainfall data sourced from BOM Barwon Heads Golf Club WS No. 087135.

A comparison of 2015 monthly total rainfall and the average monthly total rainfall (2001-2015), including when the estuary mouth was closed.

The average annual rainfall (2001-2015) was 543mm, the 2015 total rainfall was 466mm. The highest total rainfall was recorded in January (68mm).

Date: 03/02/2015 Estuary mouth state: CLOSED

Date: 10/08/2015 Estuary mouth state: CLOSED Photo: 01/08/2015

Date: 23/10/2015 Estuary mouth state: CLOSED Photo: 30/09/2015

Date: 12/12/2015 Estuary mouth state: CLOSED Photo: 05/01/2016