High and Dry
If you had been standing here 20 000 years ago, you would have been surrounded by dry land. The west coast of Australia was somewhere the other side of Rottnest!

Flooded!
The Peel Inlet formed 6000 years ago when sea levels rose and flooded large areas of the coastal plain.

The land where you are standing would have been underwater, part of a 2 kilometre wide tidal channel which covered much of the land where Mandurah now stands.

The estuary was flushed with sea water and marine animals thrived.

Fresh and Salty
Sea levels were similar to today. There was little tidal flow. In winter, fresh water flowed in from rivers, diluting the salt water of the estuary.

During summer, salt levels would become higher than sea water. Many marine animals would have been unable to live in the water because of these fluctuations in salinity.

Silting Up
4000 years ago, the floor of the estuary was uneven, with underwater hills and valleys carved by the channels of rivers. Gradually these features have become covered with 1 to 3 metres of silt so that the floor of the estuary is even.

Smelly!
After colonial settlement (1829), land was cleared, fertilizers were used, cattle, sheep and pigs were farmed. The levels of nutrients such as nitrogen and phosphorus washing into the estuary increased.

The shallow water, combined with the increased level of nutrients created a perfect environment for algal growth. By the 1970s, the estuary was smelly and choked with algae.

The Solution
A reduction in fertilizer use by farmers, and the digging of the Dawesville Channel has reduced the volume of algae.

The Channel has increased the tidal range, and the estuary is flushed with sea water. Marine plants and animals are increasing, while estuarine species are becoming less common.