In 2006/07 didymo continued its spread throughout South Island waterways. Meridian views the spread of didymo as a significant risk for the natural ecology of New Zealand. We continue working with government agencies, councils and other organisations who share our concerns. We maintain close consultation with these groups with a shared focus on further research and monitoring, on sharing information among stakeholders and on public education. To this end, in December 2006 Meridian worked with Biosecurity New Zealand to jointly organise and host a didymo forum where key information on didymo and its possible effects on hydropower generation, irrigation, tourism and recreation were discussed. A wide variety of stakeholders and participants attended from New Zealand and Australia.

Impacts of Didymo

Meridian is very concerned about the possible environmental impact of didymo on the Manapouri and Waitaki catchments and on our operations there. Didymo is present in both catchments and also within the Ohau C canal in the Waitaki catchment at a microscopic level. The Ohau C canal and the other Waitaki hydropower canals are especially vulnerable to didymo, which may flourish in the environment provided by the canals. We continue biological and engineering research to prepare for the likely prospect of hydropower plant upgrades to combat the threat of didymo in order to maintain our continued operations. Extensive didymo surveillance and monitoring programmes are also in place for the Manapouri and Waitaki Power Schemes in accordance with our permits issued by Biosecurity New Zealand.

Mararoa River diversion

During 2006/07, Meridian extensively consulted with stakeholders in the Manapouri catchment area to determine the methods that are acceptable to all parties to allow a staged resumption of the Mararoa River diversion into Lake Manapouri while minimising the risks of further didymo spread. The consultation was extremely valuable and resulted in agreement on appropriate strategies and methodologies. Following the consultation process, Meridian applied to Biosecurity New Zealand for permits to allow a staged resumption of the Mararoa River diversion. This application was approved in August 2007 and rediversion will re-commence once the required permit obligations have been met.