Just over 1km from the centre of town (off the Hansen Bay Lookout Rd) lies Lake Thetis. It is estimated the lake became isolated from the sea about 4800 years ago when sea levels dropped and coastal dunes formed around the Lake.
The lake is one of only a few places in the world with living marine stromatolites, or 'Living fossils'. The microbes that build stromatolites are a species of cyanobacteria and are similar to those found in 3500 , which are the earliest record of life on Earth. The lake's stromatolites that look like rocky lumps have been dated to about 3370 years old. Stromatolite communities grow as the this layer of bacteria on their surface deposit calcium, cementing sediment into bulbous structures. Blister mats of cyanobacteria can also be found growing on the margins of the lake in the flood zone. These mats are sensitive and easily disturbed.
The stromatolites are easily accessible during the drier months when the water level is at its lowest. The best examples can be found at the south-western edge of the shoreline but they are brittle and visitors are asked to look, but don.t touch.
Lake Thetis is isolated from major surface drainage and is fed by groundwater flow. The only loss of water comes from evaporation. It is a saline lake but there is no evidence to suggest the lake has a connection to the sea. The water level fluctuates around average sea level but doesn't appear to reflect tidal variations. The lake levels follow trends more closely related to the rainfall for the area.
The lake water is alkaline and nutrient poor but provides an ideal environment for bottom dwelling microbial communities. The lake contains some small fish, amphiods and a few crustacean species adapted to living in highly saline environments.
The circumference of the lake is only 1.2 kilometres and provides an interesting and enjoyable walk. Please stay on the path provided.