The Eric Singleton Bird Sanctuary is just eight kilometres from the Perth CBD, flanked by busy roads and suburbia on three sides.

But once you are inside the wall of trees that surrounds the wetland, the city sounds quickly recede.

"You start to hear the birds in the background, the sound of the traffic starts to go as you walk through the wetlands, and at dusk you can start to hear the frogs as well," Jeremy Maher, the manager of sustainability and environment at the City of Bayswater, said.

Just five years ago, what is now the bird sanctuary was a degraded wetland with major algal blooms on the surface for much of the year.

Map The Eric Singleton Bird Sanctuary takes water from Bayswater Brook, sends it in a horseshoe-shaped path, then feeds it into the Swan River.

It is named for Eric Singleton, who saw the value of the wetlands in the 1970s and was instrumental in saving the site from development.

In 2014 the city and the Department of Biodiversity, Conservation and Attractions began a major restoration project to transform the wetland into an area that was not only a sanctuary for birdlife, but which also sought to dramatically improve the water quality.

Jeremy Maher says the success of the project is "super exciting". ( ABC Radio Perth: Emma Wynne )

"What we saw was ... the continual decline of wildlife in there, particularly bird species," Mr Maher, who led the restoration project, said.

"In the wetland itself it was very unattractive when the thick filamentous algal bloom covered the water."

The plan was to transform the space into somewhere that was an attractive place for birds (and the public) to visit and feed clean water, free of the nutrients which feed algal blooms, into the Swan River.

Following major earthworks, the sanctuary is now a carefully crafted landscape, which takes water from Baywater Brook and sends it flowing through a horseshoe-shaped watercourse, cleaning it along the way, before discharging it back into the brook and ultimately into the Swan River.

So how does it work?

Water from the Bayswater Brook first goes through a system of underground pipes and a large gross pollutant trap.

Water flows from the Bayswater Brook into the sanctuary where it sits in a pool to allow sediment to settle. ( ABC Radio Perth: Emma Wynne )

"It's about the size of a small office and takes out all the Coke cans, cigarette butts, sediment before it enters the wetlands," Mr Maher said.

"Two hundred litres per second comes into the site and three quarters of that just goes straight back to the brook.

"The other 50 litres per second just goes into the wetland and into a sedimentation basin.

"When the water hits the basin, it stops and becomes still, and that pulls out all the sediment which then go into the base of the wetlands.

"Then every five years we will come along and clean it all out."

A walkway through the horseshoe shaped waterway allows the public to enter the bird sanctuary. ( ABC Radio Perth: Emma Wynne )

From the initial basin the water flows, imperceptibly slowly, through the horseshoe waterway.

"Then through the rest of the wetland, we have profiled it to have deep and shallow areas and these change the amount of oxygen in the water — it's a process called denitrification, which helps to strip nitrogen out of the water," Mr Maher said.

Finally, the whole area has been planted with local native reed-like plants, baumea articulata, which further absorb nutrients from the water.

In the shallow areas, long legged birds can walk and search the mud for food. ( ABC Radio Perth: Emma Wynne )

In addition to stripping nutrients, the varying deep and shallow sections have created habitats for a range of bird species.

"In the shallow section we come across the long, skinny-legged birds, like the spoonbills and herons, that like to walk around in the water and use their long beaks to dig around in the mud and pull out their food," Mr Maher said.

In the deeper, open water at the end of channel, black swans have returned and begun breeding, realising one of the goals of the restoration project.

"They were here last year and had their cygnets and I've seen a pair here again, which I think are nesting," Mr Maher said.

Regeneration happens quicker than expected

The growth of vegetation has surprised even Mr Maher.

"The density and growth is probably a couple of years down the track of what we thought it would be by now," he said.

As hoped, black swans have returned to the wetlands since the restoration. ( ABC Radio Perth: Emma Wynne )

While it is a largely manmade environment, the bird sanctuary is now functioning well on its own.

The restoration cost was $3 million but "maintenance costs of this wetland isn't actually that much more than it was before, apart from the sucker truck that comes in once a month and takes out all the gross pollutants from the trap," Mr Maher explained.

"That is because we have got to the point where we have a nicely balanced, functioning wetland.

"This is the end of summer when wetlands are normally experiencing their worst water quality, that's when the algal blooms are showing the most.

"You can see that we don't have any in here, the birds are happy and feeding and so forth."

Native reeds from the baumea species blanket the sanctuary and draw nutrients out of the water. ( ABC Radio Perth: Emma Wynne )

Attention has now turned upstream and transforming the drains that feed into the wetlands into healthier living streams.

"This has been a project that I have been lucky enough to be a part of over four years, and those were the years when my children were born as well," Mr Maher said.

"I used to come down with them as babies as the project was being built and I still come down with them on weekends, so they have seen it grow and it's a nice little connection for me."