Rivers, lakes, streams and ponds

Sunday 12 September 2010 was the day for our pilot survey of a water body.  A stretch of the River Wye close to the town was chosen and ten of us waded in to see what we could find.


By the time it gets to Rhayader the Wye is a fast flowing upland-river some 30 metres wide, wider when in flood.  The banks here are mainly lined with trees of alder and sallow with sessile oaks on drier banks.  Beneath the bank-side trees in the flood zone is a 1-2m wide fringe of greater woodrush with occasional patches of reed canary grass in more open areas.  The pretty American alien plant pink purslane is frequently encountered in this river-edge zone.  The river bed is of exposed bedrock often boulder strewn and with deeply cut and scoured sections interspersed with frequent lengths of shallow riffles. Rocky banks fall shear to deep water in places while elsewhere particularly on the insides of bends shingle beds are deposited which when exposed at times of low flow form beaches up to 15m wide.  The fast flow and low nutrient status of the water results in a generally stony river bed virtually devoid of any obvious plant life.  Occasional plants of the greater water-moss Fontinalis antipyretica clinging to submerged boulders are the only obvious green plants.

With nets and trays to tip our catch into we started listing our findings.  Mayfly larvae, of a number of species, were particularly numerous and the larvae of a few species of caddisfly and stonefly were also well represented.  Water mites, thin round-worms, midge larvae, a small leech, three species of aquatic beetle and river skaters were among the other varied invertebrates. We hoped to find the fresh-water limpet but found only a long empty shell.  Fish caught included several small minnows, a bullhead, a salmon par and twelve stone loaches which for the small amount of time spent searching suggested that quite good numbers of fish were present.  A dipper flew past and a grey heron stalked the shallows downstream of our designated 50m sample stretch.  We were all pleasantly surprised by these initial findings and expect to find a good deal more when we undertake more detailed surveys throughout next year.


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