Some flooding is good for health of the river

ROD Mackenzie’s article (Cod in danger, Sunraysia Daily, November 11) highlights important concerns about blackwater in the River Murray.

Blackwater is a natural process that happens in river systems; however, as Mr Mackenzie points out, it’s not always the result of completely natural events.

The River Murray floods have happened from heavy rain and some floodplains are seeing water for the first time in decades.

However, like many rivers in Victoria, the Murray River is a “working” river, it doesn’t function as it did naturally. 

River regulation, based on supplying water important to towns and farming, reduces the frequency of floodplain flooding, increasing the build-up of organic material on the floodplain and the risk of hypoxic (low oxygen) blackwater events when floods do occur.

Environmental water managers, like anglers and the general community, are really concerned about the impacts of blackwater.

After all, environmental water is used specifically to benefit native fish such as Murray cod in many places, such as the Lindsay River, Mullaroo, Gunbower and Lower Broken creeks.

There are plans to extend the duration of the natural flooding at Barmah in the coming weeks, using environmental water.

This will support the plants, fish and waterbirds in the lowest lying wetlands in the forest and it will have no impact on the blackwater that is already happening because the organic material has already been washed off the floodplain from the high natural flows.

The hypoxic blackwater that we’re seeing is from significant rain across the region, not environmental water. The cause of the blackwater has been unavoidable, but daily monitoring and flexible water management is helping to limit the impacts of it. 

Just as land managers carry out frequent cool burns to avoid one big hot, damaging bushfire, waterway managers try to reduce excessive leaf litter build up on floodplains with regular flooding to avoid or reduce the short-term negative impacts of blackwater events.

 Contrary to Mr Mackenzie’s comment, environmental water managers have had no influence on the extent and duration of flooding at Barmah Forest this year, nor has water been artificially held on that floodplain. 

The percentage of native fish caught in creeks and wetlands was much higher (40 per cent) in 2015-16 than in 2014-15 when it was just five percent. This is why it’s so important to continue supplying environmental water. 

Denis Flett,

Victorian Environmental Water Holder chairperson

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