Strategies for managing the lakes of the rotorua district, New Zealand

The Rotorua district in New Zealand contains 12 nationally important lakes. Environment Bay of Plenty (EBOP), which has the responsibility of managing the quality of these lakes, set a routine monitoring program for these lakes and adopted the method of Bums et al. (1999, 2000) to analyse the data and calculate a numeric Trophic Level Index (TLI) value for each. In 1994, the district community indicated a goal to maintain the present condition for most of the lakes and to improve the remainder. As a result, numeric baseline TLI values were written into the Proposed Regional Water and Land Plan as the Rotorua District lake-water quality objectives. This plan also required formation of a community action plan for the remediation of any lake that exceeded its baseline TLI, a criterion that targeted five lakes. Deterioration in the water quality of these lakes is linked to urban expansion and gradual conversion of forested land to pasture over the past 100 years. Draft action plans identifying causes of lake deterioration, together with possible means of solving the problems, have been published for four lakes. Annual reports on the state of I each lake have been published since 2000. This lake management system has resulted in valuable communication between EBOP, the Rotorua District Council and the communities living around the lakes, and has been instrumental in obtaining a cooperative approach to solving the identified problems. Methods to remediate these lakes include: converting pasture back to forest; alum dosing; creating riparian strips along streambanks; developing wetlands; installing reticulated sewage systems, and; diverting wastewater inputs from a lake into nearby forests.