Water testing results from the Darling-Baaka River at Menindee indicate the river is “chronically sick” and raise concerns about the health of the Murray-Darling basin, experts say.
The New South Wales Environment Protection Authority released the second round of test results days after the state government declared it would investigate the deaths of millions of fish at Menindee in far-west NSW as a “pollution incident”.
The latest results were from seven samples collected by WaterNSW and the EPA on 30 March. Five were taken at Menindee and two downstream at Pooncarie.
High levels of ammonia were detected in samples collected on 21 March, five days after the fish kill began. One detected ammonia at 56 times higher than the national guidelines for fresh and marine water quality.
Dr Ian Wright, a professor of environmental science at Western Sydney University, said the first results showed a toxic level of ammonia and it was heartening to see that the levels had decreased.
“It’s … up to five times higher than it should be at some sites but it’s nothing like the 56 times that it was before,” he said.
Wright said nitrogen and phosphorus levels were still “sky high”. The EPA said it suspected the high nutrient levels were due to the rotting fish. .
“The system is supercharged with nutrients,” Wright said. “I think it’s a chronically sick river and it doesn’t take much to tip over.”
That nutrient load led to algae blooms, he said: “I don’t know if a lot of these problems are manageable. The nutrients reflect everything that’s going on, right up into Queensland, all over New South Wales. It’s a massive catchment … all soil erosion, fertiliser, animal wastes, sewage.”
Blue-green algae was detected in both sets of samples. An amber alert remains in place for the river at Menindee and Pooncarie. This means people should not drink untreated water but there are no restrictions on recreational use such as swimming.
Wright advised people against having contact with the water when an amber alert was in place. “When you’ve got a fish kill, there’s likely to be bacteria, as in faecal bacteria,” he said.
In response to concerns raised by Wright about the first round of test results – which included not testing for certain bacteria – the EPA told Guardian Australia that more samples had been taken on 4 and 11 April and would be tested for bacteria.
“The first round of testing on 21 March was to respond to the emergency and the immediate concerns around pesticides,” a spokesperson said. “Additional testing rounds will investigate other potential causes.”
The EPA also clarified the number of water samples taken, in response to criticism about a lack of samples. Six samples were collected on 21 March by WaterNSW, seven on 30 March by WaterNSW and EPA officers, five on 3 April by WaterNSW, two on 4 April by EPA officers, and six on 11 April by WaterNSW.
Wright said he was happy to see sample sites added at Pooncarie but there still were not enough.
“We’re not seeing results upstream from well above the fish kill,” he said.
The results were an important reminder of how “finely balanced” river health could be.
An EPA spokesperson said it had access to upstream data from WaterNSW: “The … investigation is continuing and water quality data from before the fish kill will form a part of that investigation.”
