Water quality in many of the Rotorua-Te Arawa lakes has declined slightly over the past year, according to latest annual monitoring results, highlighting the importance of long-term sustainable water quality solutions.
The Trophic Level Index (TLI) for the lakes is measured annually and provides a measure of lake water quality. TLIs are calculated using four separate water quality measurements – total nitrogen, total phosphorous, water clarity and chlorophyll-a.
Latest water quality results show improvement in just three of the 12 lakes over the past year (2014/15), with the remainder either stable or declining. Bay of Plenty Regional Water and Land Plan have TLI objectives for each of the Rotorua Te Arawa lakes, with 10 of the 12 lakes currently not meeting their TLI targets.
Bay of Plenty Regional Council Lakes Operations Manager Andy Bruere says lake water quality can fluctuate for a variety of reasons.
“Water quality can be impacted by things such as climatic conditions and rainfall. Although many lakes reached their TLIs last year (2013/14), this year TLI’s were impacted by a warm, settled summer. This was particularly true for lakes Rotorua and Rotoehu, which saw a decline in water quality.
“To compliment the TLIs, we have a number of different scientific monitoring systems that measure the environmental quality of each lake. These systems include cyanobacterial (algae) monitoring, live monitoring buoys which collect data on lake water quality 24/7 on some of the lakes, native and introduced fish monitoring, as well as water chemistry testing.”
Improved water quality was recorded in lakes Okaro, Rerewhakaaitu and Tikitapu, while previously improving levels in lakes Rotorua, Rotoehu and Rotoiti declined this year. Stable water quality was recorded in lakes Ōkataina, Ōkāreka, Rotoma and Rotomahana, while further long-term deterioration was recorded in lakes Tarawera and Rotokakahi.
Mr Bruere says this year’s results reinforce the importance of long-term thinking for improving water quality.
“There has been significant work into lakes restoration over recent years with the long term trend for many lakes improving, as indicated by some of our lakes reaching their targets last year. The decline in TLI for some lakes (not withstanding climatic variations) highlights the importance of long term sustainable solutions to protect water quality. ”
“The decrease in water quality levels for 2014/15 by no means takes away from the work done to-date, or its importance. Rather, it reinforces the fact that there is no quick or easy fix for cleaning up our lakes, but that action must continue for the benefit of our community, the environment and our economy.”