G’day fishos! I was lucky enough to be invited to an environmental recent water information session held in the Albury City Council building.
Discussion involved a few areas, but environmental flows and how they benefit the river system and surrounding wetlands was the main focus. Blackwater events got a big chunk of the discussion and I must admit, I learnt quite a lot.
I suppose I already knew that floods were a good thing for the whole ecosystem, but I wasn’t aware just how important they are and how regularly rivers need to flood to keep things healthy.
I also wasn’t aware how much Lake Hume and Dartmouth Dam have “flood proofed” the Murray, and how they are one of the main contributors to the fish kills we see due to these blackwater events.
I didn’t realise there was such a thing as good blackwater, as well.
High and medium “flushing” events used to occur pretty much every year prior to Hume and Dartmouth being built.
Hume cut back those flushes dramatically and Dartmouth reduced them by another 60 per cent, creating the perfect base for “hypoxic blackwater” to occur.
Blackwater occurs when organic carbon is released from soil, sticks, bark, grasses and leaf litter once flood plains are covered in water for a few weeks.
It results in tannin or tea colour water that carries essential nutrients into rivers and over the flood plains which results in a healthy river system.
Hypoxic blackwater occurs when dissolved oxygen levels fall below 2 milligrams per litre.
This causes fish kills, and is a result of too much leaf litter combined with wetlands being covered for too long at a time when temperatures are too high.
That’s why we need regular flushes timed to eliminate this problem.
Considering the big red gum forests that exist in our major wetlands lose 80 per cent of their leaf matter if they haven’t had a decent drink in four years, it’s imperative that environmental flows take place on a regular basis.
Significant flows below Yarrawonga that will cover wetlands enough to make a real difference have to happen, and happen over a period of a few weeks.
We’ve witnessed two massive fish kills in the last seven years and this will be the norm if we don’t get meaningful environmental flows regularly.
If you see a forum of this kind advertised in a town near you, I’d certainly recommend you get along.
It gives you great insight into what’s needed to keep our rivers and our fishery healthy.