Two environmental issues have dominated the news this election year - and both have focused on our waterways.

Serious storms and flooding - and the resulting economic costs - have focused attention on the effects of climate change, while events like the Havelock North Water Inquiry have fuelled ongoing discussion about the state of our waterways.

The Paris Climate Agreement, which New Zealand has ratified, aims to limit global warming to no more than 2C to reduce the future risks of sea level rise and extreme weather events. But do politicians and the public really understand the future cost if this target is not achieved?

Important for New Zealand is the fact that as climate changes, so does the frequency and magnitude of floods and droughts. With current warming trends we can expect a greater frequency and intensity of extreme events. This means more floods and, perversely, more droughts. Floods have always ranged in magnitude, measured in terms of their probability of recurrence (for example the "100-year" flood), but previously rare large floods are expected to become more common.

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We have also built on our floodplains, drained our wetlands and cut down large tracts of forest, all of which serve to exacerbate both the flood hazard and the exposure of our towns to risk.

The political problem is that no matter what we legislate in terms of "greenhouse gas" emissions, the climate will continue to change because we are living with the consequences of a global phenomenon.

The issue for voters is that, to date, none of the major political parties has addressed the need to be proactive in responding to these consequences in a sustainable way.

Resilience in all our communities needs to be enhanced, especially in coastal communities where the risk posed by rising sea levels is very real. While reducing emissions is important, it is only one, small part of the problem. Dealing with the inevitable impact of climate change is the real issue we need to tackle.

Ultimately, we have very little control over the quantity of water flowing in our rivers. But we have a far bigger role to play when it comes to the quality of that water, and there is no reason why effective legislation can't be put in place.

While floods destroy infrastructure, homes, towns and lives, deteriorating water quality also has the potential to do considerable economic harm and presents a hazard to human health. The state of New Zealand's rivers is a matter of national disgrace. Every major political party appears to recognise this.

The topic has been highlighted by debate surrounding the Government's recently announced goal to make 90 per cent of rivers swimmable by 2040. The quality of our rivers is, however, multi-faceted, and not simply determined by the level of E.coli, or other bacteria, entering our waterways.

A major pollutant in our rivers is often overlooked. It is what turns them brown when it rains: soil and sediment. These particulates can also bind with phosphorous, which together with elevated nitrogen in the water (strongly associated with nitrates from intensive dairy run-off) fertilises algae. Algae then blooms in abundance, consuming dissolved oxygen in the water during the daytime, killing other aquatic life.

Sediment on its own also destroys river habitat, with fine sediments clogging spaces between stones on riverbeds. In some rivers, sediment has changed the form and shape of entire waterways, which negatively affects the habitats available for native fish and invertebrate species. This also makes flooding worse, because the river has less capacity to transport flood flows.

Sediment comes from erosion in the river catchment, which is a serious issue in some parts of the country. Again, while the political parties offer solutions to water quality using their own definitions, a key challenge for the next Government is to address this problem in a holistic way.

A joined-up, whole-of-catchment approach is required where water chemistry, bacteria loading, sediment and habitat are all taken into account.

New Zealand needs good policy that deliberately, effectively, and sustainably tackles these issues to build a more resilient and healthy environment for generations to come.

Ian Fuller is an Associate Professor in Geography with Massey University's Institute of Agriculture and Environment.