But a million trees and farmer buy-in is helping a Kiwi hero restore its water quality.
Shannon Te Huia did something not so long ago he hasn't done for years – went swimming in the Pūniu River.
As a kid Te Huia would often join his whānau and friends to swim and picnic along its banks: "Our uncles would take car-loads of us and we'd all meet at the river. It was a beautiful environment," he says.
But over the years the now 40-year-old civil engineer watched as the waters of the Waikato river suffered increasing degradation from thousands of tonnes of sediment estimated to have run into it from surrounding land – and gradually the days of diving in for a swim came to an end.
"I can't really say why this was happening, but it wasn't good," he says. "The river used to be clear but it developed a brown tinge and looked like Coca Cola. It got so bad we used to be able to smell it before we saw it."
Then six years ago Te Huia, who grew up close to the river at the Mangatoatoa Pā near Te Awamutu, decided to do something about it. He formed Pūniu River Care (PRC) with the aim of restoring the 57km river - a tributary of the Waipā River - as close to its former pristine state as possible.
With input from farmers and many others in the community PRC is turning things around. It employs around 40 local people, has planted about a million trees along the river, established a commercial nursery growing up to 1.5 million trees a year and helped return the river to a condition good enough for Te Huia to go swimming again.
"The last time I swam was last summer," he says. "It was good to do because I've had some of the best moments in my life out there in nature."
His work on the iwi-led project has been recognised nationally, earning him the 2021 Kiwibank Local Hero of the Year at the New Zealanders of the Year awards.
Te Huia says it was his training as a civil engineer which gave him the confidence to tackle such a project. He says Māori believe the river is a living entity and that there is a relationship between its health and the health of the people.
"We formed PRC because it was something practical we could do and planting trees seemed the most simple and effective way to clean the water, stabilise its banks and reduce the sediment getting into it which was turning it muddy and dirty.
"We are focusing on the entire catchment and the tributaries and streams that flow into the Pūniu," he says. "It is not a job that can be done in two hours on a weekend which is why we've created the PRC model (it is an incorporated society and charity and, in addition to money it earns commercially, receives funding from local and central government and the Waikato River Authority)."
All the trees have been grown at the nursery PRC established at the Mangatoatoa Pā. "We've got over 40 staff employed in planting, nursery and maintenance and we also run a commercial operation and sell trees to farmers and the public.
Te Huia says a lot of manuka trees have been planted along with many varieties of grasses. PRC also focuses on fencing off waterways and wetlands to keep stock out (a task it mostly sub-contracts out), weed spraying and pest control.
At its top reaches the river flows past sheep and beef farms while further down in its journey dairy farms are the predominant land use. Te Huia says PRC has support from most of the farmers - and others in the community.
"A lot of the farmers we went to school with and they share the same memories. They want to stop (degradation) from occurring too. We are a small community and everyone has a genuine desire to improve their farming systems; they too value the waterways, the birdlife and the beautiful things about nature."