Swan River Reefs Bring Back Fish After Century of Damage

Two hundred years after settlers stripped a million tonnes of limestone from Australia's Swan River, the ecosystem is finally healing itself.

The Nature Conservancy started rebuilding the riverbed in 2023, dumping limestone back into areas around Attadale and Freshwater Bay to recreate the shellfish reefs that once made the Derbal-Yerrigan (as the Noongar people call it) a vibrant estuary. Between the 1920s and 1950s, builders hauled away the river's natural limestone foundation, leaving behind nutrient-heavy mud that has degraded water quality for decades.

"A lot of the base of the river was built of historical shellfish reefs," says Brett Dal Pozzo, marine restoration manager at The Nature Conservancy. Each shellfish can filter litres of water daily, providing a natural cleaning service the river desperately needs.

The team created 6 hectares of new reef and seeded it with 160 tonnes of mussels grown in nearby Cockburn Sound. While a hot summer initially killed many mussels, the reefs have bounced back beyond expectations.

Today, mussels, oysters, and scallops cover the restored sections. Snapper and other recreational fish species now use the reefs as breeding grounds, bringing marine life back to waters that had become ecological dead zones.

The Ripple Effect

The project does more than bring back fish. The shellfish naturally filter out excess nutrients that fuel harmful algal blooms, helping the river adapt to climate pressures. As temperatures rise and weather patterns shift, these living reefs work around the clock to keep water cleaner.

The conservancy is now testing reef structures in shallow water to protect disappearing sandy beaches. These artificial reefs absorb wave energy before it reaches shore, reducing erosion that threatens both riverfront homes and vital habitats like seagrass beds.

The work shows what's possible when communities invest in restoration rather than accepting environmental loss as permanent. What took decades to destroy is being rebuilt in years, proving nature can recover when given the right support.

The Swan River's renaissance offers a blueprint for estuaries worldwide facing similar challenges from historic resource extraction and climate change.