This web-based report summarises Otago Regional Council (ORC) monitoring results in Catlins | Pounawea Estuary since 2008.

ORC monitors 15 large estuaries across the region following methods outlined in the National Estuary Monitoring Protocol, and newer approaches like ‘sediment plate’ monitoring. Catlins/Pounawea Estuary (hereafter Catlins Estuary) is relatively large (~830ha), and is classified as a shallow, intertidally-dominated estuary. It discharges into the Pacific Ocean through a permanently open tidal mouth located east of the small settlement of Pounawea. The estuary has two main freshwater inputs, the Ōwaka River that flows from north of Pounawea into the eastern basin near the entrance, and the Catlins (Pounawea) River that flows from the west into the area known as Catlins/Kuramea Lake (hereafter Catlins Lake). Compared to the eastern basin, Catlins Lake is muddier, shallower and more susceptible to nutrient problems due to poor flushing.

The catchment and the estuary margins have undergone significant modifications since European settlement. In the early 1900’s most of the lower catchment, including the land bordering the estuary, was cleared for farming, and large areas of wetland and salt marsh bordering the estuary were also drained and reclaimed. Further changes include the construction of Hinahina Road bridge in the middle of the estuary, and hardening of the estuary margin for erosion protection.

State of the Environment (SoE) monitoring of Catlins Estuary has been undertaken by ORC since 2008. ‘Broad-scale’ habitat mapping surveys were undertaken in 2008, 2012, 2016, 2021 and 2023, detailed ‘fine-scale’ surveys in 2016, 2017 and 2019, and sedimentation monitoring annually at two sites since 2016. In addition, targeted investigations have been undertaken to evaluate sediment quality and biota within different habitat types, and to assess historical seagrass and salt marsh extents. Monitoring has shown a decline in the health of the estuary over time.

Switch between survey ‘Monitoring locations’ and ‘Catchment land use’ classifications using the top right toggle. When ’Monitoring locations’ is selected (the default), the map shows the estuary outline, the area where broad-scale intertidal habitat mapping occurs, and labelled points that denote site-specific fine-scale and sediment plate monitoring sites. When ’Catchment land use’ is selected, the map shows land use classifications (LCDB5 2018) in the surrounding catchment. For more information hover over features and/or drag and scroll on the map to move and zoom in on areas of interest, respectively.

The Catlins and Ōwaka rivers drain a combined catchment area of ~ 410km² with the dominant land cover high-producing grassland (62%) primarily used for sheep and beef grazing, with smaller areas of dairy present (see Figure 1). Exotic plantation forestry accounts for 5% of the total catchment area, with the largest area within the Catlins (Pounawea) River catchment. Pastural land uses and exotic forestry are known sources of fine sediment and nutrients, particularly during high rainfall which can lead to increased run-off.

The chart below shows monthly mean flow for Catlins and Ōwaka Rivers. The vertical lines indicate the dates when SOE monitoring was undertaken. Hover over the lines to see flow values.

Disclaimer

Information displayed on this web site may be provisional and may not have been checked using the Otago Regional Council’s Quality Assurance procedures. The Otago Regional Council do not make any warranty, expressed or implied, or assume legal liability or responsibility whatsoever for the accuracy or completeness of this information. Further, it does not make any representation whatsoever that the information provided is fit for any particular purpose.