Mat Dalby, Denmark Bulletin

Wilson Inlet/ Nullaki is a resilient estuary despite high nutrient loads from the catchment but water quality will become more variable between years due to climate change.

A Department of Water and Environmental Regulation report, Wilson Inlet (Nullaki) – Condition of the Estuary 2025, was tabled at the Wilson Inlet Community Science Forum held on November 19 at the Denmark Country Club.

Department officials presented the report which assesses the main drivers of estuary health that includes rainfall, river flows, catchment condition, nutrient inputs and sandbar dynamics, as well as the estuary’s water quality and seagrass pastures.

Reflecting on the impacts of climate change, the report says water quality in Wilson Inlet will become more variable between years.

While the inlet’s water is currently described as ‘good’, the report also acknowledges the ‘continuing supply of nutrients from the catchment are ongoing threats to the inlet’s health’.

Sleeman, Cuppup worst

Notably, seagrass cover decreased between 2019 and 2022, while macroalgae increased.

Despite these trends, no fish deaths were reported during the 4-year monitoring period, from June 2019 to May 2023.

Wilson Inlet is fed by five major rivers and a network of sub-catchments, of which the Sleeman and Cuppup systems remain significant contributors of phosphorus to the estuary.

Wilson Inlet Catchment Committee executive officer Shaun Ossinger said work in these areas was critical.

“In short, kicking cows out of creeks is priority number one,” he said.

“All our modelling shows that the Cuppup and Sleeman sub-catchments are significant point sources for nutrient export.”

But the nutrient sources had more to do with proximity to the inlet and soil type than farming practices.

WICC was working with landholders on practical solutions.

“If you are a farmer in the Wilson Inlet catchment, there is a range of things you can do,” Mr Ossinger said.

“Everything from soil testing, stream restoration, to how and when you apply your fertiliser can make a positive difference.”

Nutrient mapping was already driving change.

“Our data has shown that farmers are reducing the application of fertiliser, phosphorus in particular, saving themselves money and reducing nutrient export to Wilson Inlet,” Mr Ossinger said.

But urban residents also had a role to play.

“For those who are not farmers, we can still make a difference with how we fertilise our lawn.

“Joining a community planting day where we plant out on-farm waterways with native seedlings is a fantastic way to help improve the health of the inlet.”

WICC continues to collaborate with Traditional Owners through the Southern Aboriginal Corporation ranger team.

The team had assisted with tree planting, stream restoration fencing, seed collection and foreshore flora surveys.

WICC was also looking to engage the rangers to supply seed for a future nursery.

Despite the pressures on the inlet, both the report and WICC remained cautiously optimistic.

“There are many ways we can all help improve the health of Wilson Inlet,” Mr Ossinger said.

This article appeared in Denmark Bulletin, 11 December 2025.