Middle Severn Grayling

I've been fishing the Bridgnorth to Highley sections of the Severn for a few years now and some of the runs scream grayling but i've never had one, is this due to the river colouring up too much each winter? Or are they there in small numbers?

I have caught them well upstream as in wales but where is the furthest downstream they have been reported at, anyone know?

I've never caught them, or known them to be caught below the confluence of the Severn/Vyrnwy. They being a salmonid prefer cooler, clear gravelled water associated with the higher reaches of a river (Trout Zone). Hence why you’ve caught them in the Welsh uplands of the Severn.
The Severn being a long river, the further you get down it, the warmer the water becomes due to solar radiation and Heat Island effect of urban run off.