Water quality is important
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Water quality is the degree to which water is suitable for drinking, swimming, fishing and agriculture. Algae, phosphorus, bacteria, and suspended sediment are examples of what can impact water quality.
Land Air and Water Aotearoa (LAWA) use the Trophic Level Index (TLI) to monitor water quality in New Zealand. This measures four parameters (water clarity, chlorophyll content, total phosphorus and total nitrogen) to produce a final score. Over the last 10 years, Lake Dunstan has scored ‘good’ and ‘fair’. ‘Good’ is classified as having high oxygen content and low organic content where algae and other organisms are rare. ‘Fair’ is where the lake water is average due to moderate levels of nutrients and algae. View water quality data |
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Unacceptable phosphorous levels
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The 2015-2020 Otago Regional Council’s (ORC) water quality review found that Lake Dunstan recorded phosphorus levels above the acceptable limit. High phosphorus levels can cause deoxygenation of water, algae blooms and increased pollutants that can threaten aquatic ecosystems, humans and pets. As Cromwell continues to grow, the demand for wastewater treatment and agriculture could see the level increase.
The 2018 CODC 10-year management plan reports that Cromwell's water supply does not meet the New Zealand Drinking Water Standards. This is due to no protozoa and virus protection. Protozoa can carry diseases (e.g. Cryptosporidium and Giardia) which can cause gastroenteritis in humans. Viruses (e.g. Norovirus and Hepatitis A) can enter waterways from sewage runoff and could cause a variety of gastrointestinal and immune issues. |
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Dense Lagarosiphon major weed beds reduce water flow and light penetration leading to anaerobic conditions. Oxygen is removed from the environment and can create foul odours, algae blooms and a good habitat for snail parasites which cause swimmer's itch. This is the same for Sediment that is high in organic matter that can remove oxygen from the water as it decomposes.
Water from Lake Dunstan and the Kawarau Arm fill our local aquifer, Cromwell Terrace. If the water body deteriorates, this could also impact our drinking water.
Water from Lake Dunstan and the Kawarau Arm fill our local aquifer, Cromwell Terrace. If the water body deteriorates, this could also impact our drinking water.
Tackling the issue
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Otago Regional Council (ORC) is responsible for managing the region’s groundwater and surface water resources.
The Central Otago District Council (CODC) is responsible for the control of activities and their actual or potential effects on the water surface and margins of the river. Toitū Te Whenua Land Information New Zealand (LINZ) has responsibility for the management of Crown-owned lands and waterways including the bed of Lake Dunstan and associated weed/pest control programmes. Contact Energy is legally responsible for managing the visual effects in the Kawarau arm caused by its power generation activities at Clyde. |
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How to manage water qualityIn 2020, Cromwell’s population was over 7,000 and is predicted to reach over 15,000 by 2050. Improving water treatment plants is needed to ensure drinking water remains safe and sewage is correctly managed to prevent runoff into the waterways.
Sediment is an ideal environment for Lagarosiphon to grow which in turn captures more sediment. Both need to be managed to reduce their effects on water quality. Removing Lagarosiphon and managing sedimentation will reduce the risk of toxic algae blooms, swimmer’s itch, odour and dangerous pathogens. |
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What has been done
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The CODC 10-year management plan included improvements to Cromwell's water network. The Cromwell Wastewater Treatment Plant upgrade was completed in 2018 and won the Environment and Sustainability Award at the IPWEA (Institute of Public Works Engineering Australasia) NZ Annual Excellence Awards.
In 2016 LINZ created the Lake Dunstan Weed Management Committee to implement a 10-year plan to control Lagarosiphon in Lake Dunstan. Local governing bodies, stakeholders and trusts are on the committee including LDCT. Contact Energy has monitored sediment in the Kawarau Arm since 1993 but has not implemented any significant management. LDCT recently sought the legal opinion of a specialized RMA barrister to support the legal opinion that Contact Energy is responsible for the effects caused by the Silt in the Kawarau arm. This opinion was supported by the ORC. |
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What will be doneAccording to the CODC’s 10 year plan, projects to address protozoa in the water supply are to commence in 2026 and estimated to cost $4.5 million. Further projects are planned to improve water treatment, distribution and operational performance for Bannockburn and Pisa.
NIWA (National Institute of Water and Atmospheric Research) and LINZ create annual plans the ensure they undertake regular herbicide spraying and clearing. Contact energy is currently creating new plans to manage the visual amenity values and transition of the Kawarau Arm. |
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References
[1] LAWA (2021) Lake Dunstan. To view Click here
[2] NIWA (2010) Lake Water Quality in New Zealand 2010: Status and Trends. To view Click here
[3] ORC (2020) Water Quality in Otago. To view Click here
[4] ORC (2017) State of the Environment Surface Water Quality in Otago. To view Click here
[5] Ministry of Health (2019) Annual Report on Drinking-water Quality 2018-2019. To view Click here
[6] CODC (2018) 10 Year Plan. To view Click here
[7] Ministry of Health (2007) Pathogen and Pathways, and Small Drinking-water Supplies: Resources for the Drinking-water Assistance Programme. To view Click here
[8]NIWA (2016) Ten Year Management Plan for Lagarosiphon at Lake Dunstan: 2016 to 2025. To view Click here
[9]ORC (2012) Cromwell Terrace Aquifer Study. To view Click here
[10]ORC (2011) Clutha river/Mata-au Plan. To view Click here
[11] ORC (2006) Learning to Live with Flooding: A Flood Management Strategy for the Communities of Lakes Wakatipu and Wanaka. To view Click here
[12]A. Farminer (2013) People, Rivers and Recreation: Fluid Relationships of PLace and Experience on the Clutha River, Otago, New Zealand. To view Click here
[13] CODC (2021) Framing Our Future Long-term Plan 2021-2031: Infrastructure Strategy. To view Click here
Images: Unsplash & LDCT
[1] LAWA (2021) Lake Dunstan. To view Click here
[2] NIWA (2010) Lake Water Quality in New Zealand 2010: Status and Trends. To view Click here
[3] ORC (2020) Water Quality in Otago. To view Click here
[4] ORC (2017) State of the Environment Surface Water Quality in Otago. To view Click here
[5] Ministry of Health (2019) Annual Report on Drinking-water Quality 2018-2019. To view Click here
[6] CODC (2018) 10 Year Plan. To view Click here
[7] Ministry of Health (2007) Pathogen and Pathways, and Small Drinking-water Supplies: Resources for the Drinking-water Assistance Programme. To view Click here
[8]NIWA (2016) Ten Year Management Plan for Lagarosiphon at Lake Dunstan: 2016 to 2025. To view Click here
[9]ORC (2012) Cromwell Terrace Aquifer Study. To view Click here
[10]ORC (2011) Clutha river/Mata-au Plan. To view Click here
[11] ORC (2006) Learning to Live with Flooding: A Flood Management Strategy for the Communities of Lakes Wakatipu and Wanaka. To view Click here
[12]A. Farminer (2013) People, Rivers and Recreation: Fluid Relationships of PLace and Experience on the Clutha River, Otago, New Zealand. To view Click here
[13] CODC (2021) Framing Our Future Long-term Plan 2021-2031: Infrastructure Strategy. To view Click here
Images: Unsplash & LDCT
