The annual drawdown of Lake Rotoiti will start on Monday and will see the lake drop 100mm below its normal operating range.

Bay of Plenty Regional Council lowers the lake by 100mm each year as part of consent guidelines to help facilitate flushing of the Ohau Channel and reduce flood risk in the channel.

The regional council plans to hold levels at or near the drawdown limit for a few weeks (depending on weather) to facilitate surveys and monitoring and provide time for lake community feedback.

Council principal engineering surveyor Graeme O'Rourke said the council had 10-15 per cent of each year (36-55 days) to achieve this drawdown.

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He encouraged anyone with any issues or observations around Lake Rotoiti to note the details and take photos for the record before contacting the council.