Lake Waahi

Lake Waahi is located west of Huntly. It has 522 hectares of open water and a maximum depth of five metres. The lake is supertrophic, meaning it is very nutrient enriched. The water quality of Lake Waahi has improved since the 1970s and 80s following the control of coal mining activities in the catchment and the return of submerged aquatic plants. Further improvement may occur if the abundance aquatic plants continues to increase.

Lake Waahi’s catchment is predominantly pastoral. However the lake has received inflows from coal mining in the past.

The lake discharges to the Waikato River through a controlled outlet on the Waahi Stream.

Results from water quality monitoring undertaken by Waikato Regional Council show Lake Waahi is currently supertrophic, with:

• high levels of microscopic algae (phytoplankton)
• low water clarity
• high nutrient levels - near eutrophic levels.

Check out our Nutrient Enrichment of Shallow Lakes indicator and its data for Lake Waahi.

The water quality of Lake Waahi has been studied previously by the:

• University of Waikato - 1974-1976
• Waikato Valley Authority - 1981.

During the first study by the University of Waikato the lake had a healthy cover of large submerged aquatic plants (macrophytes) and clear water. During the late 1970s the macrophytes began to die off and their populations collapsed. The study in 1981 by the Waikato Valley Authority describes how the lake changed from having clear water to high turbidity and high levels of microscopic algae.

Waikato Regional Council monitored Lake Waahi every second month from September 1995 to December 2004. Monitoring during this period showed no significant changes in water clarity or in Chlorophyll a and nutrients.

Overall, the results suggest that Lake Waahi has improved since the collapse of the submerged aquatic plants in the late 1970s.

Further improvements in water quality are possible if the abundance of aquatic plants continues to increase.