The Manning River has stopped flowing above Mount George, along with its tributaries

Gravel pit: the Barnard River, a tributary of the Manning River, at Bretti Reserve. Photo: Darren Ray

Gravel pit: the Barnard River, a tributary of the Manning River, at Bretti Reserve. Photo: Darren Ray

Aquatlic ecologist, Dr Keith Bishop knows the Manning River and its catchment like the back of his hand. He has been doing regular surveys of the river for 12 years. And what he has seen recently has shocked him deeply.

Dr Bishop usually surveys at night, but this October, wanting to save travel time, he decided to camp out and look around.

"The upper valley and river are in such a stressed condition, very depressing," he said. "I am surprised how ignorant I was."

While people are well aware of the plight of farmers due to what is one of the most severe droughts in recorded history, what is currently occurring in our river system is not as well known.

I think it is important the broader community realise what is going on, so close to home.

Dr Keith Bishop, aquatic ecologist

"I think it is important the broader community realise what is going on, so close to home," Dr Bishop said.

Valley sides along the Manning River upstream of Mount George are covered by dead and dying trees. Landholders are indicating trees more than 100 years old are dying.

The river has stopped flowing in the upper-middle Manning, north of Mount George, as have most of the other rivers in the catchment, apart from the Little Manning and the Barrington rivers, but that was some months ago.

"With no trickle flows the river in shallower areas is now reduced to algae-smothered ponds lined with decaying organic material and developing layers of sludge, instead of clean cobbles and gravel underlying sparkling waters.

"There is a feeling of a strong of cesspools rather than a river, the smells are also powerful, from the decaying organic sludge, rotten-egg gas being released when you wade in and, of course, the omnipresent stench of cattle which have died and are now decaying in the heat."

Dr Bishop reports that native fish species, such as Australian bass, have now stopped breeding, with no young sighted since early 2018. Other species have stopped migrating. The decline of breeding and movement of native fish species has allowed alien species to spread upstream very quickly when small flows allow.

Dr Bishop asked landholders if they have seen conditions like this before and their answers depended on where in the catchment they came from.

Bodies of cattle are decaying on the river's edge. Photo Dr Keith Bishop.

Bodies of cattle are decaying on the river's edge. Photo Dr Keith Bishop.

"In the upper Manning, upstream from the influence of the Gloucester River which still collects water from southern rainfall events, long-time landholders say they have never seen such a climatic event before.

"In the lower Manning, which gets that water from the Gloucester River, and receives occasional showers from coastal-fringe rainfall events, long-time landholders say they have had droughts like this before, for example, in the 1960s and 1980s," Dr Bishop said.

Data from the WaterNSW website extrapolated from 190 days up to November 3, 2019 shows that the Manning River has endured 129 days of very low flow (less than 100 megalitres a day) in 2019 to that date. A graph of this data (see the story on our website) shows this is dramatically more than any other period since data was available from World War II.

The river is measured at Killawarra for level, flow, and turbidity. At the time of writing on Thursday, November 7, the river height was 0.18 metres and falling and the discharge (or river flow) was 9ML/d and falling. A very low for the Manning River is considered to be less than 100ML/d. Irrigators are required to cease taking from the river at 98ML/d.

Dr Bishop has not seen the river not flowing in the 12 years he has been surveying river.

"This is the very first time ever," he said.

"Once you get to the Gloucester River it starts to flow again, and that's downstream of where these observations are."

River flow at Killawarra for the past seven days (to November 7) shows flow has reached below 10ML/day. Very low flow is set at less than 100ML/day. Data from Water NSW.

River flow at Killawarra for the past seven days (to November 7) shows flow has reached below 10ML/day. Very low flow is set at less than 100ML/day. Data from Water NSW.

When I was interviewing Dr Bishop for this story, he indicated that morning there was 100ML coming out of the Gloucester River, but only 60ML further downstream in Killawarra.

"So there's a 40ML loss along that system, possibly due to irrigation," he said.

"It's turning into another system. If you see something of that size, there's a system change going on. Something very drastic is going on," Dr Bishop said.

"I'm not a climate modeller but it looks like a very extreme shift, potentially, if you go along with what the climate modellers are saying.

"Also very weird things are happening in the upper estuary with saltwater pouring upstream with the low flows - school prawns, garfish and silver batfish turning up at the tidal limit." The tidal limit of the Manning River is just past Wingham at Abbotts Falls. "I expect bottle-nose dolphins to appear soon and let's hope there will be no more mortalities as has happened before," he said.

Only months of water supply estimated left in Bootawa Dam

MidCoast Council estimates that if water restrictions were to remain at level three, there would be between 80-90 days of supply in Bootawa Dam.

According to Rob Scott, council's director of infrastructure and engineering services, council stopped pumping from the Manning River to fill the dam on October 11.

Bootawa Dam's capacity has been falling since that date and is currently at 90 per cent, Mr Scott said.

"It does seem like a really striking figure and for people who hear that figure for the first time it will be an absolute shock because everyone would think that we have a lot more storage than that, but our system works inherently differently to a lot of other water supplies. It's not reliant on long term river flow. What it's reliant upon is water being available in the river now because we can pretty much take any quality of water into our system and treat it up for use," Mr Scott said.

Level three water restrictions are being introduced on Monday, with stricter restrictions possibly being introduced in coming weeks.

"I don't know exactly how far we could stretch it, because we don't really know how effective it would be to amp water restrictions to no external water use whatsoever. But when the chips are really down, we would absolutely knuckle down and get rid of all external water usage and really start to restrict internal water usage," Mr Scott said.

"Exactly how far we would get out of that, at the same time, is difficult. We'd also look at ramping up the Nabiac acquifier supply."

Mr Scott said the Nabiac acquifier is now being used.

"It's well below its capacity at the moment. We're conscious of not trying to get in too early and use it all and use it to early," he said.

Council is currently in the process of renegotiating its water access licence conditions with the National Resource Access Regulator to allow it to pump from the river to "maximise their yield".

A story about irrigation is coming in the next few weeks.