Public health warnings have been issued against swimming in Okawa Bay, Lake Rotoiti. Photo / Andrew Warner
Public health warnings have been issued against swimming in Okawa Bay, Lake Rotoiti. Photo / Andrew Warner
People are being warned away from some of Bay of Plenty's most serene and picturesque swimming spots amid algae bloom and possible faecal contamination.
Research by Lawa (Land, Air, Water Aotearoa) found nine of 80 monitored Bay swimming spots too unsafe to swim due to poor water quality. Six ofthe 80 had no recent data to determine a finding.
Lawa reports on water quality sampling results from each site, as well as overall bacterial risk based on longer-term testing.
A traffic light system identifies sites suitable for swimming with a green light and those where caution is advised for young, elderly or people with compromised health with amber.
A red status warns the water is not suitable for swimming, either because the risk of infection or exposure to potentially toxic algae is too high.
In Rotorua, as of Thursday, a red status applied to Utuhina Stream at Lake Rd, Ngongotahā Stream at Railway Bridge, Ōkawa Bay at Lake Rotoiti, the Lake Ōkaro boat ramp and, in Lake Rotoehu, Kennedy Bay and Ōtautī Bay.
On Monday, Toi te Ora Public Health reissued a health warning for Ōkawa Bay at the western end of Lake Rotoiti due to "an extensive algal bloom throughout this area of the lake".
Chief medical officer of health Phil Shoemack said algae blooms could produce toxins that could be "quite harmful" to animals and humans. People could experience a skin rash, and in extreme cases trouble breathing, numbness around the mouth, fingers and lips.
"The effects from toxins from algae can be quite severe."
Toi Te Ora chief medical officer of health Dr Phil Shoemack. Photo / NZME
Shoemack said that despite the warnings, there had been a general improvement in water quality of Rotorua's lakes over the past 20 years. He credited much of this to riparian planting, fencing and lakeside properties moving away from septic tanks.
"But still from time to time, you do tend to get more blooms in water with high nutrients, often in shallower lakes with more farms in the area or urban development.
"We haven't had any heavy rain for a while . . . when you do get heavy rain . . . all the contaminants that are sitting around will get washed into our lakes, rivers and streams," he said.
Bay of Plenty Regional Council acting general manager of integrated catchments Laverne Mason said long-standing problem areas such as the Utuhina Stream fell into 11 "focus catchments" of priority.
The council has been working with local landowners to "mitigate and remove the identified contaminants".
A public health warning sign has been erected at Okawa Bay, Lake Rotoiti. Photo / Andrew Warner
"It is an evolutionary process and one that understandably takes time," Mason said.
However, while the Utuhina Stream was unsuitable for swimming long term (based on the past five years of data) at Lake Rd, the stream at its Pukehangi Rd location was fine for swimming, with some caution advised after rainfall.
Mason said regular monitoring of both Utuhina Stream sites indicated the waterway also had problems with E.coli - a bacteria found in faeces - "however the cause is not well understood".
"Further catchment survey work is planned to better understand the elevated results but they are likely to be a combination of sources including: leaky infrastructure; upper catchment agriculture; avian contamination; and domestic sources including pets.
"As this stream runs through residential Rotorua, past hundreds of properties and geothermal hot spots, this makes it quite a different issue to manage."
Utuhina Stream. Photo / NZME
Mason said land management staff worked closely with rural landowners in the upper Utuhina and Mangakakahi catchments to ensure farms were complying with local nutrient management rules and best practice.
"This has been successful and 100 per cent of the upper Utuhina Stream has been retired from stock, the majority of the main tributaries in the upper catchment that feed into the Utuhina are either retired or planted and all are fenced."
Upper Utuhina catchment landowners were also working with the council on environmental restoration projects that would improve water quality through retiring steeper and wetter areas of the farms, she said.
"We have detailed science investigations underway to pinpoint outstanding E.coli sources in both catchments and have pulled in a range of experts to help us identify and apply new solutions to reverse this trend."
The regional council has spent more than $21 million over the past three years on work to improve water quality in the Rotorua Lakes.
Lawa is a partnership between regional councils, the Ministry for the Environment, the Cawthron Institute and Massey University.
