In somewhat of a negative for the natural environment, the macro-invertebrates – crustaceans, worms, snails, spiders and insects that without a backbone – that frequent the South Esk River were nowhere to be found this week.

‘‘Given the state of the gorge, it was actually hard to find anything because they were all washed away,’’ Tamar Natural Resource Management program co-ordinator Greg Lundstrom said.

‘‘In a sense, it’s a renewal process and really does reset the system.’’

The only survivors were the ones who could cling onto or under rocks or hide in the river’s sediment.

Mr Lundstrom hosted an interactive hands-on session on Wednesday morning for ecological boffins at the Cataract Gorge basin cottage, as macro-invertebrates were used to assess the health and quality of the river.

In the wake of World Wetlands Day on Tuesday, he compared samples from the Tamar Wetlands and the Kings Meadow Rivulet with some startling conclusions.

‘‘You need flow in the river to be alive – essentially rivers will die from the bottom up,’’ Mr Lundstrom said.

‘‘In this case, there is always another lot of water in the estuary, but what it is doing is keeping a fresher system further down.

‘‘Potentially having new nutrient and other things coming in is a cleansing system.

‘‘Dilution isn’t necessarily the solution to pollution, but having pollution does mean that a lot of the muck gets cleaned out.’’