The Tywi rises within 15 miles of the Teifi in the Cambrian Mountains and a mere six miles along its 75 mile length its swift flow is interrupted the Llyn Brianne reservoir.
You can also journey down the Teifi - click here to find out more.
Surrounded by moorland and conifer forest, Llyn Brianne is periodically dosed with lime to ensure the health of the river downstream.
In the 1990s the stretch of river just below the reservoir was badly affected by acidification from acid rain and the leeching of pollutants by the surrounding conifer forest which subsequently entered the water and made the water acidic. Young fish, particularly the salmon and sea trout, are sensitive to acid water conditions and both fish and birds such as the dipper suffer because the insects and invertebrates they feed on are badly affected by acid conditions. Subsequently liming was introduced to neutralise the river's acidity and more recent studies show that salmon and sea trout numbers are increasing in the affected stretch of river.
There's plenty to see here, with torrents of boulder-strewn white water flowing into calm tranquil pools - in summer a haunt for the beautiful demoiselle, (a damselfly). The riverbanks are frequently covered by overhanging oakwoods and in the damp, bleak uplands beyond you can find common butterwort, round leafed sundew and club mosses.Downstream, situated amongst the spectacular waterfalls of the upper Tywi valley above Llandovery, a few miles north of Rhandirmwyrn, is Dinas Nature Reserve. Redstarts, sandpipers, pied wagtails and wood warblers are just some of the birds that can be found.
From Llandovery the Tywi meanders through a broad, flat valley which contains some of the richest grazing land in Wales. At Llandeilo, the Castle Woods Nature Reserve (which has been designated an SSSI) rises steeply out of the water meadows and oxbow lakes and is dominated by the ruin of Dinefwr Castle.
The woods are a fine example of mixed mature woodland comprising oak, ash, sycamore, cherry, hawthorn, and spindle. They provide cover for foxes and badgers and are alive with birds including all native species of woodpecker, treecreeper, nuthatch and marsh tit.
Across the river at Gelli Aur Country Park there's a small herd of fallow deer and the arboretum contains Monterey pine and giant redwoods. In the water meadows teal, widgeon, mallard, coot and wading birds like golden plover and lapwing are regular visitors in the spring and winter, and the valley is the only regular wintering ground in Wales for Siberian white-fronted geese.
Although most famous for its fishing, the Tywi, like its Cambrian sister the Teifi is also home to some rare fish species, the allis and twaite shads, small members of the herring family, and as a result it has been proposed as a Special Area of Conservation (SAC). The shad spawn in only a few rivers in the UK (including the Wye and the Usk) but are becoming rare in rivers due to fishing, pollution and their inability to negotiate weirs.
But the Tywi has been home to some fishy giants in its time as well. In 1933 a salmon fisherman landed a nine foot long, 388lb sturgeon the largest fish ever caught without a net in Britain - near White Mill about three miles east of Carmarthen.
The Tywi, like the Teifi, was formerly home to a fleet of coracles of a design unique to the river that were used to fish for salmon and seatrout. Unfortunately, the fishing industry on the Tywi has suffered the same fate as the Teifi's and the salmon and seatrout now provide sport primarily for anglers with few coracles left.The prevalence of oxbow lakes in the Tywi valley provides some spectacular shows through the year. In summer at Bishop's Pond in Abergwili (actually a magnificent oxbow lake formed when the Tywi flooded in 1802) there's a spectacular show of yellow water lilies on the pond when the water level drops and reed sweet grass fringes the edges - a species you'll also find nearby in the Teifi valley, further West in Pembrokeshire, on the Gower, in Powys (especially along the Montgomery Canal), on Anglesey and in several other sites along the N Wales coast.Do you have any tales from the Tywi to tell us? What wildlife have you seen on your nearest riverbank? Would you like to write about your nearest stream or river? Email us at nature.sww@bbc.co.uk or have Your Say.
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