It is indisputable that our rivers today face multiple threats from pollution[in all its forms] , predation , and over abstraction ,however I am old enough[65] to remember when many rivers , particularly in the northern industrial areas of the UK were virtually devoid of any fish or indeed any life at all . My grandfather had a farm close to the river Aire in Bingley West Yorkshire As a nipper one day he took me down to the river , it was completely black and had no life in it at all ,nothing,you couldn't even allow farm animals to drink from it .In the 60's many similar rivers in the north [ Calder ,Don , Rother ,the list goes on ] were in exactly the same state . When we went fishing we either wet a line in the Leeds Liverpool canal which was fairly productive , or travelled to the upper reaches of the Aire . Today these same rivers have fairly healthy fish populations , even runs of Salmon ,clearly this is down to the demise of the heavy industries that polluted the rivers and better sewage treatment . Currently most rivers have some fish in them but are still at threat from mans abuse of the riverine environment ,we simply don't learn from history . The depressing thing is that it doesn't have to be like this but there seems little political will to change matters .