Current State of the Horowhenua (Waiopehu) Freshwater Management Unit

The Waiopehu Freshwater Management Unit (FMU) includes the Punahau 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. 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, Punahau 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.

Punahau 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.

These are the issues Horizons is aiming to address with projects like the Arawhata constructed wetland complex.