Awatapu Lagoon is a 12.9 ha oxbow lake created when the Ōhinemataroa / Whakatāne River was straightened in 1970. The lagoon has poor water quality but provides good ecological values for birds and has high potential for restoration.
River Lake has undertook monitoring and a series of investigations to characterise the water quality of Awatapu Lagoon and identify practical options for improvement.
Improvement of water quality in Awatapu Lagoon over the long term will require multiple actions over a sustained period to reduce nutrient loads (internal and external) and enhance natural processes that attenuate nutrients. Reducing the biomass of hornwort is a high priority that would provide multiple benefits. However, maintaining some aquatic plants is also important for maintaining reasonable water quality in small natural lakes.
The report for Whakatāne District Council can be found here:
Te Awa o te Atua /Matatā lagoon is an outstanding example of a complex dune land-wetland-open-water system on a freshwater-saltwater interface. It has high botanical values and provides high value breeding and feeding habitat for a large number of water birds.
The western lagoon was remediated in about 2010, however the width of aquatic emergent wetland vegetation on the margin of the western lagoon remains considerably less than what was intended to regenerate into shallow wetland habitat following the post-flood remediation.
River Lake Ltd and Place Group undertook water quality, fish and vegetation surveys to assess the ecological health of Te Awa O Te Atua / Matatā Lagoon and identify ways to improve its values.
The report for Whakatane District Council can be found here:
Sullivan Lake is a small (2.7ha), shallow, urban lake located in Whakatāne which has had persistently poor water quality. River Lake has undertook monitoring and a series of investigations to characterise the water quality of Sullivan Lake and identify practical options for improvement.
The report for Whakatāne District Council can be found here:
RWT dye released from the Mangaone Stream to the Manawatū River, 2024.
Palmerston North City Council is in the process of substantially upgrading the treated water that is currently discharged to the Manawatū River. One option being considered as part of the upgrade is to shift the discharge location further downstream.
River Lake undertook a series of mixing studies to assess the mixing characteristics of the Manawatū River at multiple locations downstream of Palmerston North. This was done by: 1) releasing a bolus of Rhodamine WT (RWT) dye in to the river and using drone imagery to map its dispersion across the river as it moves downstream; 2) slowly releasing RWT dye into the river to achieve a steady state and using a fluorometer to measure its concentration at along cross-sections downstream.
River Lake analysed water quality from 12 Rotorua Te Arawa lakes to better understand potential causes of interannual variability of the Trophic Level Index (TLI); and explored ways to account for natural variability when expressing TLI targets.
Long-term water quality trends were statistically analysed. The report documents adjustments required for phosphorus data in order to account for laboratory analytical changes over the period 2010-2019.
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River Lake has been working with Bay of Plenty Regional Council to complete a report on the state and trends of water quality in Bay of Plenty rivers.
Over the ten year period 2009 to 2018 the Bay of Plenty river monitoring sites have shown overall worsening trends for total phosphorus (TP), dissolved reactive phosphorus (DRP) and nitrate (NNN); but overall improving trends for absorbance (A440), total ammonia (NH4-N) and electrical conductivity.
The trend results are shown in the graphs below:
River water quality trends 2009-2018
River water quality trends 2009 – 2018
The proportion of BOP river monitoring sites with improving trends (PIT) for selected variables.
Manawatu at Totara Road WWTP discharge, facing upstream.
River Lake has been working with Palmerston North City Council for many years to help understand and reduce the effects of the Tōtara Road wastewater treatment plant (WWTP).
We have undertaken monitoring of aquatic macroinvertebrates, periphyton, water quality, and diurnal fluctuation in dissolved oxygen. We have also undertaken investigations and experiments to understand river processes.
Learn about the role of nutrients in driving excessive periphyton growth in the Manawatu River, and how periphyton mine phosphorus from fine sediment captured within their mats. Click the link below:
In 2017 PNCC initiated a Best Practical Option (BPO) review of how to improve the treatment and disposal of wastewater in the future. River Lake is part of a team assisting with this process.
Here is our 2019 experimental setup to assess what concentrations of nitrogen are required to control periphyton growth in the Manawatu River.
The Ongatoro/Maketū estuary is a shallow, inter-tidal estuary located north of Te Puke. In 1957 the Kaituna River was diverted directly to sea and the influence of the river on the estuary was dramatically reduced. This resulted in accelerated in-filling from the
flood tide delta, loss of mussel beds, loss of wetlands and sea grass, algal accumulations and changes in the benthic fauna. The project sought to re-divert more of the river back into the estuary to improve the ecology and mauri.
River Lake provided science and planning input for the application to re-divert the Kaituna River back to the Ongatoro/Maketū Estuary. Keith co-ordinated and led the science input related to water quality and ecology. He jointly prepared a gap analysis, undertook investigations, prepared AEE reports relating to water quality and ecology and presented at the Consent Hearing and the the Environment Court.
Water quality and biota are strongly influenced by internal nutrient loads (e.g. sediments). An important part of the investigations was to quantify the likely internal loads compared to external loading predicted by the hydro-dynamic model. This involved measuring oxygen regimes and mapping algal accumulations.
What is the phosphorus load to Lake Rotorua and how much comes from human activity?