From the Opuha to the Kakahu - Managing water clarity

Discharge consent and water clarity limits for the Kakahu River

OWL holds a resource consent for this discharge. A key consent condition relates to water clarity and requires that the discharge must not:

• reduce downstream water clarity in the Kakahu River by more than 50 per cent after reasonable mixing,
• when water clarity in the Kakahu River is more than 1.6 metres (measured using a standard “black disc” being visible).

The reach of the Kakahu River where the discharge occurs has relatively pristine water quality, which is why staying within the limits set by the discharge consent matters for the mauri of the river, its ecosystems and the local community.

The clarity of the water in the lake is affected by the size and nature of rainfall events in the catchment.

• After heavy rain, more sediment enters the lake.
• If heavy rain occurs in the growing season, water entering the race may have higher levels of sediment.

It’s important to note that clarity outcomes depend on both the Opuha and Kakahu river systems. In practice, this means that the irrigation schemes can materially influence clarity outcomes — positively or negatively.

Why reliable water supply matters

To ensure they comply with their consent conditions, OWL must stop discharging water if it cannot be sure the discharge will stay below the 50 per cent threshold.

For those that depend on that water for their stock and irrigation, this can have a dramatic effect on:

• animal wellbeing
• the viability of their farming operations
• the well-being of the wider community.

Historically, exceedances have been relatively rare. However, unusual weather patterns during the 2025 growing season made them more frequent. With the consequence that farmers and communities are unable to access water when they needed it at a critical time for crops and stock.

Why hasn’t enforcement action been taken?

Until recently, the evidence for environmental effects that can be directly attributed to the scheme’s discharge hasn’t been robust enough to support enforcement action with a reasonable probability of success.

However, the quality of our data is set to improve. A recent ecological study has just been released by Lincoln University, and our own science team is set to undertake its own study later this year.

With better knowledge, future decisions will be better informed and enforcement action becomes a more viable option, should it be necessary in future.

Is there a solution?

A workable solution would need to meet these two goals:

• Avoid any future exceedances of the water clarity limit
• Maintain a reliable supply of water for those that need it, regardless of weather conditions in the catchment.

In late March 2026, the OWL board and stakeholders met to discuss the viability of a pipeline. This option would:

• reduce the sediment loading of water taken from Lake Opuha
• prevent any sediment from entering the water as it flows down the water race.

What happens next?

As of late March 2026, OWL has not decided to progress the pipeline proposal as per the critical path agreed with Environment Canterbury.

We have been clear that:

• if OWL cannot comply with their water clarity consent condition, they must not discharge into the Kakahu River
• they must not discharge into the Kakahu and would be operating illegally if they do so.

We will continue to monitor the situation and intend to enforce compliance as appropriate, to achieve the best outcome for the environment, for the sustainability of the resource, and for the communities affected.

This page will be updated as decisions are made about how to manage this activity sustainably — whether through a pipeline or another solution.