Blundell's Swamp at Lower Portland is among the healthiest wetlands in the Hawkesbury catchment, while Bushells Lagoon near Wilberforce is ranked with the worst for water quality, weeds and land clearing.
Ecologists were given unprecedented access to 35 floodplain wetlands, including on private property, across the Hawkesbury and Hills council areas as part of a new study commissioned by a coalition of community and civic groups.
Each wetland surveyed was given a report card based on the impact of livestock grazing, land clearing and weed infestations on water quality and habitat for water birds and native animals.
"This is a landmark report," Hawkesbury-Nepean Landcare Network local landcare coordinator Katherine Clare said.
"Armed with this information, we can empower landowners, governments, and communities to help protect these unique and valuable wetlands which sit right on the doorstep of Australia's largest city."
Hawkesbury Environment Network (HEN) secretary Christine Watson said time, money and motivation would be needed to maintain and improve the health of the catchment's swamps and lagoons.
"We must invest more in weed control, awareness-raising for landowners, and management of grazing animals to make sure these wetlands provide healthy habitats for aquatic and bird life to thrive."
Even Bushells Lagoon - which scored worst alongside Yarramundi Paddocks West - was found to attract a variety of birds, as well as bird watchers.
On the fringes of north-western Sydney, around 50 known floodplain wetlands attract threatened and migratory birds, such as the Fork-tailed Swift, Little Eagle and Barking Owl.
The Wetland Site Assessments in the Hawkesbury report was funded by a federal communities environment program grant and produced by Applied Ecology.
It gives cause for action and hope, Ms Clare said.
"The Wetlands Working Group, which commissioned this work, brings together a diverse group of passionate locals, environmental advocates and government representatives," she said.
"So many people understand the value of these Hawkesbury floodplain wetlands and want to see them flourish."
The Working Group was formed in 2018 and includes representatives from Hawkesbury City Council, Hawkesbury Environment Network and Hawkesbury-Nepean Landcare Network.