This page covers work by Horizons Regional Council and partners to improve water quality and aquatic health for the Horowhenua-Waiopehu Freshwater Management Unit (FMU).
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The Horowhenua (Waiopehu) FMU includes the Lake Horowhenua, Wairarawa (Waitārere), Waiwiri, Ōhau and Waikawa catchments in the south of the Horizons Region. Waterways in this FMU face pressure from intensive land use activities such as agriculture and urban development, wastewater and stormwater discharges, water abstraction for human use, and invasive freshwater weeds. Lakes and estuaries are particularly sensitive to pollution. Lake Horowhenua (Punahau) is a shallow coastal lake in the FMU that receives water from several streams, groundwater and drains that run through and under the Levin township and agricultural land. In pre-European times, Lake Horowhenua was a clean water supply, local taonga and valued fishery for the Muaūpoko iwi who lived in the coastal forest that surrounded the lake. However, the clearance of coastal forest, draining of swamps, intensification of land use, urban expansion, and the disposal of treated effluent in the lake between 1962 and 1987, led to significant degradation. Lake Horowhenua continues to receive large amounts of nutrients and sediment in addition to the ongoing internal processes influenced by past discharges into the lake. Water quality is poor as a result and the lake is regularly closed for recreation in the summer due to the potential presence of toxic cyanobacteria. The lower reaches and estuaries of the Ōhau and Waikawa streams are also vulnerable and suffer from eutrophication as a result of upstream land use activities.
Explore the current state of the FMU in an interactive StoryMap
Lake Horowhenua is a shallow coastal dune lake and the largest natural lake in the Manawatū-Whanganui Region. In 2013, Horizons Regional Council installed a continuous water quality monitoring buoy in the lake, and since then water samples have also been collected by boat or helicopter, usually on a monthly basis.
Lake Horowhenua has a single outflow to the sea, the Hōkio Stream, and receives water from several waterways, including the Arawhata, Pātiki and Mangaroa Streams.