Flow to mitigate against toxic blackwater threat

The North Central Catchment Management Authority (CMA) is kickstarting plans to mitigate against potential toxic blackwater outbreaks in parts of the Loddon River.

Overbank flooding on the Loddon in spring resulted in large amounts of organic matter, such as leaves and wood, washing down from the floodplain and higher up the banks and into the river.

The organic matter is now decaying, and can result in low dissolved oxygen levels, which can cause fish to die.

"Floods can benefit rivers such as the Loddon, but they can also have negative impacts," North Central CMA Environmental Water Manager Louissa Rogers said.

"Natural floods can reach bank levels environmental flows can never do, but in a regulated and dammed system like the Loddon, high flows can be few and far between.

"So, it's important when flooding does occur, to keep an eye on things and react accordingly, to ensure the health of the river is not affected.

"While there is no guarantee an environmental flow will stop a blackwater event, it can lessen the likelihood of one happening."

Ms Rogers said the North Central CMA will begin a flow of up to 70 megalitres a day downstream of the Loddon Weir near Serpentine until the end of spring.

"The aim of the spring flow will be to keep the river moving and wash away organic matter. If the water stays stagnant, it can become toxic, which reduces oxygen levels and fish will struggle to survive," she said.

"Adding flows now can also turn the carbon in the water into vital nutrients for animals and plants.

"It is important over summer and autumn to ensure pools remain fresh and connected to allow water bugs, fish and platypus to move between them. From December to May, the flow will decrease to up to 50ML a day.

"Healthy storage levels have resulted in high allocations, and managing a river like the Loddon in a wet year is different to managing it when it's dry. We have the opportunity to use the water allocated to build resilience over summer, keep fish alive by connecting pools and give the vegetation a drink during the hottest time of the year.

"All this will benefit the river in the coming years. We realise that no one benefits from a dead river."

The river flow is authorised by the Victorian Environmental Water Holder, in line with its Seasonal Watering Plan 2016-17. The Loddon system section of the plan was developed in collaboration with the North Central CMA and in partnership with the Department of Environment, Land, Water and Planning, GMW and community representatives.

Regular updates are posted on the North Central CMA website www.nccma.vic.gov.au.