Rivers not necessarily clean after flood

OVER the past week rivers and streams have continued to fall, albeit rather slowly in most cases. Some of the smaller streams have dropped to good fishable levels, whereas the big rivers will take some time yet to get back to normal.

The Taieri in its upper reaches actually rose this week before starting to drop again and it will probably be a couple of weeks before it gets to summer level, provided there is no more rain.

Conventional wisdom says that rivers get a good cleanout with a flood but that is not necessarily so. Pollutants on the land are flushed into rivers and some of the pollutants remain in the water when the flood recedes. Silt is a pollutant in high quantities and chemical pollutants can bind with silt and remain on the river bed.

Rivers can be at their cleanest when they are very low, especially if they are springfed as the pollutants slowly leach way and only pure water is joining the flow. Floods also rip out weed beds, which normally harbour the creatures that trout feed on, and when it is sunny weed releases oxygen into the water which sustains plant and animal life found there.

On the Shag River the other day I was walking along a farm track about 100m from the river and the deeper ruts on the track were still full of water from the secondbiggest flood in the past 30 years. The water was only a few centimetres deep but there were hundreds of bullies up to 7cm long trapped there, which shows there must be a lot in the river. No wonder the trout in the Shag grow to a good size and are usually in good condition.

I fished the Shag at the weekend, having last fished it at the end of October, and the recent 400cumec flood made some reaches unrecognisable with banks severely eroded and pools filled with gravel. Trees have been washed away and others are lying in the river channel — it was like fishing a new river. Turning over stones, I saw lots of immature mayfly nymphs, which survive floods by burrowing down into the gravel.

I did not see as many fish as six weeks ago but enough to keep it interesting. The deeper pools were still a little misty and I probably missed some. I saw very few rises, although the fish I did spot were feeding steadily on subsurface food. One of these fish was lying towards the tail of a ripple picking off nymphs as it swung from side to side. It picked off my nymph first cast and made a dash for the trees on the far side then came rushing back and buried itself in a weed bed. It took a while to get it out by getting straight downstream of it and applying as much pressure as I dared. After that it came easily to the net and then I returned my best fish of the season so far.