Algal bloom the first in 10 years for Lake Rotorua

Algal bloom the first in 10 years for Lake Rotorua

5 November 2020

It’s been 10 years since the last substantial algal bloom was recorded for Lake Rotorua, which occurred in 2010 near Hamurana. A small bloom was recorded near the Ohau channel in 2015. The recent health warning for the toxic algal blooms in Lake Rotorua has reminded the community that there is still work to be done to improve the water quality.

“Unfortunately, the lake has been subject to high nutrient loads from intensive land use and sewage in the past and this legacy of pollution will take decades to recover. Everyone in the community needs to play their part, and that includes being mindful of how they are contributing to the water quality,” said Bay of Plenty Regional Council Rotorua Catchments Manager Helen Creagh.

Historic and current land use, past wastewater disposal into the lake and climate change are just some of the factors that impact the quality of the lake. Climate change is causing prolonged, warmer temperatures which increase the likelihood of toxic algal blooms. 

Under the Rotorua Te Arawa Lakes programme, there are both short and long term strategies in place to improve the lake water quality. This includes regulations and incentives to reduce nutrient loss into the lake through changes in land management.

Alum dosing has helped improve the water quality over the past 10 years by preventing algal blooms like the one we have now. However, alum dosing is a short term strategy which involves treating incoming streams with alum (commonly used in treating drinking water) which reduces the impact of phosphorus on the lake and the frequency of toxic algae blooms.

Long term, sustainable land use in the catchment is the solution to a healthy lake and the Regional Council is working with Te Arawa, landowners, and the Rotorua Lakes Council to ensure that this change is delivered and that alum dosing is minimised.

“Everybody can play their part to protect the lake so that it is thriving for future generations,” Ms Creagh said.