Fresh data has revealed alarming news about New Zealand's rivers, with two-thirds of monitored sites rated poorly for harmful E. coli.
The data published by Land, Air, Water Aotearoa (LAWA) on Sunday morning looked at more than 1500 rivers and around 200 lakes.
It wasn't just rivers that had bad results, 60 percent of monitored lakes in New Zealand were being hampered by algal and plant growth arising from elevated nutrient concentrations.
Some of the results, published on the annual World Rivers Day, showed small signs of improvement in some areas but they highlight the work still needed to be done to turn the trends around.
"A lot of work is underway to improve freshwater, the reports released today serve as a reminder of the need for continued attention and action," Cawthron Institute freshwater ecosystems manager and scientist with the LAWA project, Dr Roger Young said.
"While the risk of toxic effects from nitrate and ammonia is limited to a small percentage of sites, data up to June 2022 reveals that impaired ecological health and elevated E. coli contamination is evident at almost two-thirds of monitored sites.
"We know that indicators of ecological health take some time to respond to restoration efforts, while some indicators of river water quality can respond more quickly to change. We are seeing encouraging signs of improving clarity and phosphorus in our rivers with an increased number of monitored sites in the A and B state bands and fewer sites in the poor D band over the last 10 years."
The data showed two-thirds of the monitored river sites were graded in the lowest two categories (D and E) for E. coli - a bacteria that can cause vomiting or diarrhoea.
It also showed E. coli levels were at the highest in rivers surrounded by urban and pastoral land while sites near native and exotic forests were in comparably better health.
"With urban streams typically receiving the worst health scores, the impact on our urban communities becomes pronounced," Dr Young said.
"Although urban streams make up just one percent of the country's total river length, their wellbeing directly affects a majority of New Zealanders, given that 9 out of 10 residents live in urban areas."
Waikato Regional Council Senior Water Scientist Dr Mafalda Baptista, who has been analysing the data, said there is not one monitored lake shallower than 10 metres in "very good condition".
Dr Baptista said a key observation is the "vast majority" of monitored lowland shallow lakes are in poor or very poor condition.
"We have taken a fresh approach to understanding lake condition nationally by evaluating the Trophic Level Index of lakes by depth and altitude," Dr Baptista said.
"There is not a single monitored lake shallower than 10 metres in very good condition. We take heart in our upland lakes, most of them are in a fair or good condition.
"Looking at the state of lake health indicators at a national level, over 60 percent of monitored lakes [92 lakes] have ecological communities impacted by algal and plant growth arising from elevated nutrient concentrations, with subsequent reduced water clarity."
LAWA Project Chair Dr Tim Davie said the findings are backed by 1.8 million data points, each representing physical samples later analysed in labs and reported by councils.
"We are starting to see the impact of challenges such as COVID-19 lockdowns on our ability to access the state and trends at some sites, and it shows how vital the regularity of our field staff's sampling is to being able to understand New Zealand's precious freshwater," Dr Davie said.
