Lake Wairarapa

Lake Wairarapa is the largest lake in the Wellington Region, with an area of 7,850 hectares. It is very shallow – only around 2.5 metres at its deepest point – and is considered to be isothermal, which means that it remains at a constant temperature throughout its depth. Pastoral land cover makes up just over 50% of the lake’s existing catchment area and is generally located to the north and east of the lake. Indigenous forest and scrub makes up the remainder of the catchment and is largely associated with the Rimutaka Range to the west of the lake.

Historically, Lake Wairarapa and the surrounding wetlands were an important source of mahinga kai and even in present times the area still has significant traditional and spiritual values and is considered a taonga. The lake also provides habitat for a wide variety of plant, fish and bird species, including rare and threatened species. The high ecological values associated with Lake Wairarapa are recognised in the Proposed Natural Resources Plan for the Wellington Region, with the lake listed in Schedule A2 as being a lake with outstanding indigenous ecosystem values.

The lake has been significantly modified through flood protection and drainage activities carried out under the Lower Wairarapa Valley Development Scheme (LWVDS). The most significant changes took place in the 1960s and 1970s and included the diversion of the Ruamāhanga River from the lake and drainage of vast areas of wetlands. Barrage gates were also installed at the outlet of the lake to regulate water levels. The LWVDS is considered to have had major socio-economic benefits in terms of flood protection and development of land for agricultural use. However, it is also considered to have had significant negative impacts on the lake ecosystem and surrounding wetlands.

Lake Wairarapa is the only lake in the Wellington Region that is routinely monitored by the Greater Wellington Regional Council. Assessments for water quality commenced in 1994 and are attempted on a quarterly basis at three sites in the lake. However, due to strong winds safe access to the sites is not always possible.