Hawke’s Bay lake pollution among the worst in the country

Lake Rotonuiaha, near the Waiau River in Wairoa, is one of the Hawke's Bay lakes tested in a study on lake pollution undertaken by the Cawthron Institute and GNS Science. Ngati Pāhauwera Development Trust, Hawkes Bay Regional Council, volunteers and landowners have been working together to improve the lake's health. Photo / Lakes380

A study of pollution in New Zealand’s lakes has found that 90 per cent of Hawke’s Bay’s lakes are in poor or worse condition, one of the worst three regions in the country.

Lakes380 - Our Lakes’ Health: past, present, future, a five-year research project led by Cawthron Institute and GNS Science, found that 45 per cent of lakes in Hawke’s Bay were “very poor”, 40 per cent were poor and 5 per cent were worse than “very poor”.

Only 8 per cent were “fair”, while 1 per cent were considered “good”.

This was the second-worst result in the country, only slightly behind Taranaki and similar to Gisborne.

One of the Hawke’s Bay lakes looked at by the study is Whakakī Lake, a 400ha coastal lake near Wairoa

According to Lakes380, the lake is in a degraded state and experiences frequent algae blooms.

The study said Hawke’s Bay Regional Council, farmers and the Ministry for the Environment through the Freshwater Improvement Fund are fencing and planting around the lake.

Programme co-leader Dr Susie Wood of Cawthron Institute said over 80 per cent of lakes in the North Island and 45 per cent nationally are in poor or very poor health.

The study aligns closely with the dismal findings of the Ministry for the Environment and Statistics New Zealand’s Our Freshwater 2023 report last week, which showed 45 per cent of lake monitoring sites worsened between 2011 and 2020 and 45 per cent of New Zealand’s total river length is unswimmable, according due to risk of bacterial infection.

“Nutrients are leaching into our lakes, sediment is smothering the lakebeds, non-native species are irreversibly changing their ecology and they are being overtaken by algae blooms. As a result of this degradation, these lakes are losing biodiversity and many are no longer safe to swim in or harvest food from,” Wood said.

She said that even then it was still not too late to make big changes to save lakes from even bigger ecological tipping points.

She said the programme was now seeking further funding to develop better monitoring tools and systems, and innovative new restoration solutions.

Programme co-leader Dr Marcus Vandergoes of GNS Science said the work involved going beyond sampling the water and sediment in the lakes, collecting and analysing lake sediment cores that could provide the history of a lake dating back more than a thousand years, pre-human arrival in Aotearoa New Zealand.

Vandergoes said they now had a good platform to build on to support restoration action.

The research used a combination of sample data and modelling and involved organisations including GNS Science, Cawthron Institute, Te Herenga Waka Victoria University of Wellington, Otago University, Auckland University, Matana Consulting, Waka Taurua Consulting, and international researchers from the UK, USA and Australia.

They closely worked with four iwi groups too, Ngāti Koata in Te Tauihu, Ngā Puna Rau o Rangitīkei in Rangitīkei district, Ngāti Kahungunu ki Wairarapa & Rangitāne o Wairarapa in Wairarapa, and Te Rūnaka o Ōtākou (Kai Tahu).

Researchers from the study physically sampled 320 of Aotearoa New Zealand’s naturally formed lakes, while 152 lakes are already monitored by local authorities or land managers.

Researchers modelled the rest to complete an analysis of 3738 lakes over 1ha in size.