• Chris Benfield takes an enlightening tour of Tamar trouble spots and talks to the Westcountry Rivers Trust.

ROSS Cherrington kicks his wellies into the bed of the Tamar, a couple of miles north of Launceston and a cloud of sediment spreads downstream. 

He is demonstrating how run-off from agricultural land, and bank erosion accelerated by other changes in the environment over recent decades, have filled in the spaces in the gravel where salmon might want to lay eggs.

There are probably dozens of other reasons why the Tamar, along with most English rivers, has seen a near-catastrophic drop in salmon numbers since the good old days — which came to an end, probably, in the 1970s. 

Tamar tributaries are similarly affected, although the Lyd and the Lynher are better than most.

Ross, farmer and fisherman, a surprisingly rare combination, is senior agriculture adviser to the Westcountry Rivers Trust, which keeps up a fight for river health in this region, thanks largely to European funding.

Nobody knows what would happen if we left the EU.

He is our guide on a tour of Tamar troublespots, followed by a discussion, organised by the WRT and billed as the Tamar Fisheries Forum. 

A small group of anglers and land owners has turned out on a dodgy-looking Sunday to meet the WRT’s head of fisheries, Bruce Stockley and other environment business professionals, at Roadford Lake.  The lake itself, along with other extractors of water, is one of the likely problems which gets a mention when Bruce outlines the state of play.

Then there are the things which happen at sea: some obvious, some mysterious, all beyond the reach of most of us.

But conditions have changed in the rivers too, thanks to all of us.

Flood prevention, which we now regard as a right, continues to change flow patterns dramatically. 

The foreign invader Himalayan balsam takes advantage of change and sets up vast colonies, smothering all competition. 

It looks lovely when it is flowering pink and full of bees but it dies back in winter and leaves bare soil to wash away, taking seeds downstream with it to start another outbreak.

And all the effort and money that has gone into paying farmers for ‘stewardship’ — losing a bit of productivity in the interests of the environment — has done almost nothing to stop soil and soil dressings washing into the rivers, according to Ross.

‘Politicians tend to think that if there are fewer dead dogs and shopping trolleys in the water in urban areas, then it’s better all round,’ he says.

‘But I wouldn’t swim in the Tamar, even up here, and a friend of mine won’t even let his cattle drink it.’

There is no point in just asking farmers to do better, he says. 

They are out of time for voluntary effort.  This is dairy country and a typical dairy farmer with 150 milkers is currently heading for a £150,000 drop in income over a year. 

He is not going to build another slurry pit, or plant ground cover to hold the soil together after cutting his maize crop, unless we pay him to do it — or fine him for not doing it.

As far as Ross knows, there has not yet been a prosecution for, for example, the kind of shortcut ploughing which delivers a skipload of soil into the river. 

The Environment Agency, somebody points out, has two river bailiffs for the whole of north and east Cornwall.

Bruce Stockley sums up at the end of the day:  ‘It has been said before that we don’t need to manage fish. 

‘We need to manage people.’

He is looking into ways in which voluntary effort might make a difference and promises to circulate some proposals for discussion.

There is no doubt in his mind that anglers are part of the solution rather than the problem, on the whole.

‘The more people we can get coming to fish, the more people there are who care about the rivers.’

• Read more from Chris Benfield at http://tinyurl.com/nfe2s7d/