From our Chair: The delicate state of the Ashburton Lakes

I’m sure that for many of you the Ashburton Lakes/Ōtuwharekai are a favourite destination to spend a day or two out of the city and reconnect with nature.

It’s a wonderful part of the country, with the big Canterbury sky stretching over the hills and the iconic lakes themselves.

The state of the lakes

Environment Canterbury Chair Jenny Hughey

Environment Canterbury Chair Jenny Hughey

Sadly, however, the natural beauty of these lakes belies a serious environmental issue that must be urgently addressed.

A recent report commissioned by Environment Canterbury and the Department of Conservation found that these lakes face a very real and immediate risk of ‘flipping’.

Flipping is when a healthy lake with clear water and an abundance of waterborne plants becomes murky and dominated by algae. It’s caused by an increase in the level of nutrients such as nitrogen and phosphorus in the water. These nutrients promote the growth of algae.

The algae affect the level of light reaching the lakebed. The plants become shaded out and increasingly struggle to compete with a growing algae population.

The problem is exacerbated by the plants being less able to dampen down the waves on the lake shore. This increases shoreline erosion and sediment going into the lake.

All this can set a lake on its way to flipping.

Our research shows that this is the very process that is underway with the Ashburton Lakes/Ōtuwharekai. The water quality is deteriorating rapidly in some cases, with Lake Clearwater a particularly serious case.

The way forward

It can be extraordinarily difficult to bring a flipped lake back to a natural state, even if the nutrients and sediment are reduced, so we need to take steps now to prevent this from happening. 

The research reveals that it is a combination of agriculture, human activity, and, to a lesser extent, birdlife that is affecting the nutrient levels.

Environment Canterbury is a member of a working group set up by papatipu rūnanga to urgently find a way to protect these precious lakes.

We know that it will take a collective effort between farmers, iwi, the local council, statutory agencies, and recreational lake users to get the required results.

We also know that we can’t take a one-size-fits-all approach. The circumstances for each lake are different. We’ll need to study each one individually and work out the nutrient reductions required.

We’re currently speaking with partners to work out what tools can be developed to support those whose activities may be contributing to the nutrient levels in the lakes.

Too precious to lose

There is much to be done and it’s vital that we act swiftly. No one wants to see these iconic lakes become so degraded. They are for all Cantabrians to enjoy. As well as their recreational value, many are culturally significant taonga to Canterbury rūnanga.

Letting these wonderful Canterbury lakes that are enjoyed by so many degrade beyond repair would be an unacceptable legacy to leave to the next generation.