Paraparaumu author and environmental historian Catherine Knight's latest book is called New Zealand's Rivers: An environmental history.

Dr Knight said she wanted to write a book that would be rewarding for her as a researcher and writer as well as meet a need, preferably on a national scale.

She consulted Professor Tom Brooking, a leading environmental historian, who suggested rivers, because there was a need to fill a gap in the environmental history scholarship to better inform the debates about fresh water going on today.

"While there is a range of environmental history scholarship on other parts of our environment such as our forests, our coasts, and our towns and cities, there is virtually nothing on rivers and other water bodies," Dr Knight said.

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"Few people understand our complex history with rivers. Yet rivers are central to our identity as New Zealanders, shaping our lives and providing the water that is so critical to our lives and economy."

The book, which took two years to write, explains how, after nearly two centuries of exploiting our rivers for personal and public gain, we have arrived at a crisis point where many of them are too polluted to swim in.

It examines the richly textured relationship between Maori and awa (rivers), how European settlers perceived and used rivers, introduction of trout and salmon and the role of acclimatisation societies as earliest advocates for our rivers, hydroelectricity schemes which reached their peak in the Think Big era, recreational boating including invention of the jet boat on our unique braided rivers, the environmental movement and protection of rivers, the impact of agriculture on rivers, the efforts of Maori to assert mana (authority) over their awa through Treaty claims and other means.

Dr Knight didn't know a lot about rivers before embarking on the project but this gave her a sense of strength.

"It meant I could bring a level of objectivity that someone with a deep-seated passion for rivers might not be able to bring to the subject."

Her research brought lots of interesting surprises including factual ones.

"I didn't know there were nine hydro stations and eight dams on the Waikato River, or that for a while the government was seriously considering damming the Huka falls to make electricity." And ones that made people reflect on current discussions about fresh water.

"It may surprise people to know that farmers were one of the first groups in society to complain about the pollution of streams and rivers, first in the early 20th century in Otago and other goldmining regions, where goldminers put their goldmining waste [tailings]into waterways.

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"This raised river beds and silted them up, making them more prone to flooding, covering surrounding farmland with thick layers of silt.

"A bit later, farmers complained about flaxmillers putting their waste into rivers in flaxmilling regions such as the Manawatu, clogging up rivers and making the water less suitable for stock.

"Flaxmillers and other polluters such as dairy factory owners got really worried, and asked the government to pass legislation to stop farmers from obtaining injunctions on them to stop their discharges, because they were worried they would be put out of business."

Dr Knight said it was beyond her expertise or scope of the book to make recommendations on what specific measures needed to be taken to improve the health of rivers.

"But I can say that for us to find solutions and make them happen, we need to begin with open, honest conversations, informed by facts and information that can be understood by all New Zealanders.

"In the book, I talk about the criticism often levelled at the policy discussions taking place around fresh water, that these are very technical, and laden with jargon and language that is inscrutable for many New Zealanders.

"Yet there are few things that New Zealanders care about more than the ability to swim in their local swimming hole, therefore they must be able to understand and take part in the discussions around ensuring their future health."

The book is among a group non-fiction finalists for the New Zealand Book Awards 2017.

"I'm very pleased with it."