Lake Rotoiti control gates unlikely to have affected water quality

Tuesday 23 March 2004 Twenty years of artificially controlling water levels in Lake Rotoiti is unlikely to have had an impact on water quality, a new report says.

Dr Ian Hawes of the National Institute of Water and Atmospheric Research (NIWA) was asked by Environment Bay of Plenty to find out if a control system installed in the early 1980s had affected the lake’s ecology.

In a report to last week’s regulation and monitoring committee, Dr Hawes says the installation of the Okere Gates “is unlikely to have measurably affected” algal growth. The gates, which control water flow from Lake Rotoiti into the Kaituna River, are operated in a way that reduces the risk of lakeshore flooding without creating problems for recreational boaties.

Environment Bay of Plenty’s control regime has reduced the natural variations in lake levels. Before, these would have fluctuated an average of 20cm within a season and between 20 and 50cm from year to year, Dr Hawes reports. That range is now much more narrow.

In earlier years, the stronger “tidal” effect may have kept aquatic weeds down in the shallower, more sheltered areas of the lake. On the other hand, stable water levels may allow wetlands to develop more vigorously, Dr Hawes adds.

Regulation and monitoring committee chairman Ian Noble hopes the report will allay some people’s concerns that water level control encourages algal blooms. It was commissioned to help the community sort management options for improving water quality in Lake Rotoiti later this year.

Environment Bay of Plenty’s Paul Dell, coordinator of the Rotorua Protection and Restoration Action Programme, says some members of the community have been worried about the impact of the gates and other lake control structures on both water levels and lake water quality.

Mr Dell says these issues will need to be worked through with the community. In the meantime, a review will be carried out of water level changes related to the installation of the Okere Gates, as well as of the weir in the Ohau Channel, which links Lake Rotorua to Lake Rotoiti.

ENDS

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