Williams River Care Association members hope results from their own study along the Seaham Weir Pool stir up more official action over their concerns about the impacts of boating on water quality.
That stretch of the Williams River downstream from Clarence Town plays a major role in supplying the Lower Hunter with drinking water. Hunter Water has said about half the water in Grahamstown Dam is pumped from the river at Seaham Weir.
But Brian Ness, the association's vice president, argued despite the group having spent many years pointing out the deteriorating water quality in the weir pool due to boating turbulence, little had been done.
"We're basically being ignored by Hunter Water and the state government generally," Mr Ness said.
To bolster its argument, the association set out to further test the impact power boats had on turbidity, and, in affecting the sediment in the river, on phosphorus and nitrogen levels in the weir pool.
"The reason we're looking at nitrogen and phosphorus is because we understand they are the main sources of nutrients for blue-green algae growth and other surface vegetation," Mr Ness said.
On January 17, Brian Ness collected water samples at two sites in an area used by power boats. One set was collected in the wakeboarding zone, and the other at a point where only higher-speed skiing is permitted under a Transport for NSW boating management plan for the weir pool.
Brian Ness said he collected one set at 6am to 6.30am, before boats were on the river. Then, for comparison, another set was collected 4pm to 4.30pm, when, Mr Ness estimated, a power boat was passing the sites every 10 minutes.
Those samples were sent to the ALS laboratory in Sydney for testing.
Brian Ness said according to the results, turbidity levels rose 1195 per cent in the skiing area and 4025 per cent in the wakeboarding zone after boating activity.
"That's a lot, but we knew that it would be of that order, because the water goes from pretty clear to muddy," he said.
The phosphorus counts increased by 60 per cent in the skiing-only zone, and 157 per cent in the wakeboarding area. Nitrogen concentrations rose by 50 per cent in the skiing area, and 100 per cent in the wakeboat zone.
Mr Ness said he believed a lot of the problem was boats' turbulence causing re-entrainment of phosphorus and nitrogen in the sediment: "They lift it off the bottom of the river and spread it through the water column."
Brian Ness conceded this was only a preliminary study, given the small sample set, but he hoped the findings prompted Hunter Water to do further research.
"We're not trying to say we've got the conclusion, we're saying, 'You guys, get off your backsides and do it yourselves".
Association members paid for the laboratory testing, which cost about $1000. Brian Ness estimated a larger, independent study would cost no more than $10,000.
Mr Ness said given the weir pool's role in supplying drinking water, "it doesn't make sense" that the government allowed for recreational power boating to continue on this part of the river.
"It seems to us the common interests of Newcastle's water users are being sacrificed, at least partially, to the personal recreational interests of a very small number of skiers and wakeboarders," he said.
Mick Godfrey, a long-time riverside resident and wakeboarder, skier and boater, had doubts about the association's study.
"Any study done by your own body is like marking your own test, so you've got to take it with a grain of salt," he said.
He conceded there had been an increase in boating activity in the permitted area along the weir pool, particularly when COVID restrictions came in, and those movements created turbidity.
But the samples were taken on a Sunday, and Mr Godfrey said the results would have been different if the tests were done during the week, when there were fewer boats on the weir pool.
He argued weather and environmental factors could also stir up the water.
"I've seen the same turbidity when the wind blows the right way," Mr Godfrey said.
Mr Godfrey said he wanted to work with the association, "to have a balance", so boating could continue on that reach of the river.
Williams River Care Association president Digby Rayward said it was time for Hunter Water and the government to act.
"The evidence is confronting, and it's clearly having a negative impact on the weir pool, and therefore on Grahamstown Dam," he said.
A spokesman for Hunter Water assured the drinking water it supplied remained safe, with "robust" processes in place to manage what was pumped into Grahamstown Dam from Seaham Weir.
"The long-term deterioration in river water quality as a result of erosion on the Williams River is a concern to Hunter Water," he said.
"We appreciate and acknowledge the latest study by Williams River Care Association. We have conducted studies through UNSW's Water Research Laboratory, among others, that show the nutrient load and erosion are contributing to deteriorating water quality."
The spokesman said Hunter Water had been working for many years to improve practices in the Williams River catchment to protect water quality.
"While Hunter Water has a major interest in the sustainable management of the river," he said, "we do not have any specified legislative or regulatory responsibility for the management of the river."