Lake Waipu

{{Use New Zealand English|date=April 2024}}

{{Infobox body of water

| name = Lake Waipu

| length = {{convert|700|m|abbr=on}}

| alt = Aerial view of Lakes Waipu and Oraekomiko

| caption = Aerial view of Lakes Waipu and Oraekomiko 2021-22

| image_bathymetry = {{Infobox mapframe |area_km2=0.07|point=none|shape-fill-opacity=0|stroke-width=1}}

| caption_bathymetry =

| alt_bathymetry = Lake Waipu

| location = North Island

| coords = {{coord|-40.045|175.158 |region:NZ_type:waterbody |display=inline,title}}

| type = dune lake

| inflow =

| outflow =

| pushpin_map = North Island

| pushpin_map_alt = Location of Lake Waipu

| catchment = {{convert|527|ha|abbr=on}}

| basin_countries = New Zealand

| image = Lakes Waipu and Oraekomiko.jpg

| area = {{convert|7|ha|acres}} (open water)

| width =

| depth =

| max-depth = {{convert|4.7|m|ft}}

| volume =

| residence_time =

| shore =

| elevation =

| frozen =

| islands =

| cities = Rātana Pā

| reference =

| other_name =

}}

Lake Waipu, just south of Rātana Pā,{{Cite web |title=Lake Waipu, Manawatu-Wanganui |url=https://www.topomap.co.nz/NZTopoMap/nz47218/Lake-Waipu/ |access-date=2023-06-29 |website=NZ Topo Map |language=en}} is a {{Convert|7|ha|abbr=on}} shallow coastal aeolian, or dune-dammed, lake. Horizons Regional Council has monitored water quality in the lake since 2015. The lake's catchment is mainly pasture and Rātana's treated sewage runs into a tributary of the lake, accounting for the trophic level index being eutrophic at 6.9. However, the submerged plant indicator of 34.3% is better and {{lang|mi|kākahi}} (native freshwater mussels) live in the lake.

A $1.75 million project with the Ministry for the Environment, Rangitīkei District Council, Ngā Wairiki Ngāti Apa, Rātana Community Board, and the Department of Conservation,{{Cite web |title=Lake Waipū Water Quality |url=https://www.lawa.org.nz/explore-data/manawatū-whanganui-region/lakes/lake-waipū/ |access-date=2023-06-29 |website=Land, Air, Water Aotearoa (LAWA)}} will pipe the wastewater to land near Whangaehu beach. Planting and other improvements it is planned to improve the lake's pollution.{{Cite web |title=Lake Waipu Improvement and Rātana Pā Wastewater Treatment Project |url=https://www.rangitikei.govt.nz/district/projects/lake-waipu-improvement-and-ratana-wastewater-treatment-project |access-date=2023-06-29 |website=www.rangitikei.govt.nz |language=en}}

Lake Waipu usually drains through the sand, as does nearby Lake Oraekomiko, though in places, especially in wet weather, a stream runs {{Convert|2.2|km|abbr=on}} to the Turakina River.{{Cite web |last=Dr Alex James and Dr Mike Joy |date=May 2009 |title=Prioritisation for restoration of out-flow stream habitat of coastal wetlands on the west coast of the ManawatuWanganui region |url=https://envirolink.govt.nz/assets/Envirolink/644-hzlc64.pdf}}