Water management

Water is vital to our business as it is essential to our 100% renewable generation sources – hydro and geothermal.  

We have a long heritage with the Waikato River dating back nearly a century as it is home to our eight hydro dams which make up the Waikato hydro system. This drives our strong commitment to the environmental health and well-being of the river for all.

Lindavia Intermedia

Government scientists have identified the algae Lindavia intermedia in a number of North Island lakes including Lake Taupo. It was identified in South Island lakes in 2004 and there has led to a sticky bloom known as lake snow, that can look like slime on fishing gear and boat hulls and cling to swimmers. There is no evidence of it affecting the health of the waterways, but it’s important to prevent its spread. We’re asking everyone who enjoys the rivers and lakes of the central North Island to follow the Ministry for Primary Industry’s guidelines when moving between waterways.
Learn more

Environmental Management


Our hydro plants produce about 10% of New Zealand’s electricity.  We aim to achieve maximum efficiency and optimal output from the hydro system in line with resource consents. The water we use for hydro generation is not consumed by our activities and remains available for other users.


Our central North Island geothermal power plants produce around 40% of our generation. Across our geothermal sites, all geothermal fluids used through our stations are injected back into the reservoir to maintain the sustainability of those resources.

We are strongly committed to understanding, managing and minimising any impacts as a result of our operations. We work closely with iwi, the community and local government to ensure we understand the effects of our operations. Some of the activities we carry out to meet compliance include hydrological analysis, geomorphological studies and ecological monitoring. We have demonstrated a strong and consistent compliance record, and in 2015 we achieved full compliance with the Waikato Regional Council for hydro operations for the second year running.

In December 2014 we entered into a long-term agreement with Tuwharetoa Maori Trust Board in respect to the storage of water in Lake Taupo. Lake Taupo is the primary source of Mercury’s Waikato hydro storage, and through the agreement we have committed to working with the Trust Board into the future.


We recognise and respect the close links that iwi have with water, including the tupuna awa relationship held by the Waikato River iwi. We acknowledge and respect Te Ture Whaimana o Te Awa o Waikato.

Our partnerships with tangata whenua are very important to our business, and we work closely with iwi, hapu and marae in our operational areas, discussing how we manage natural resources in these areas, particularly water.

In the spirit of partnership, we look for mutual mana enhancing opportunities, and support a range of programmes, such as educational initiatives, environmental and ecological restoration projects and a range of Māori cultural initiatives.

Environmental Management

We are a key partner of the Waikato Catchment Ecological Enhancement Trust (WCEET), which funds projects that protect and enhance the ecology and biodiversity of Lake Taupo and the Waikato River. 

With our support the Trust has completed, or has underway, over 180 projects since its inception in 2003, to the value of $3.7 million. Learn more about the WCEET




Water Policy

We actively contribute to water policy and reform at a regional and national level, and have regular constructive discussions with Government and local authorities on fresh water management, and participate in collaborative and consultative processes. 
In recent years these contributions have included taking part in the national Land and Water Forum, the Ministry for the Environment’s consultation “Next Steps for Fresh Water”, the Waikato Regional Council’s Healthy Rivers / Wai Ora: Plan for Change and “Let’s Talk Water”, the Waikato Regional Council’s Fresh Water Discussion.