Robbie Northman is perhaps the most brilliant of our region's young anglers, certainly in my book.

He's intelligent, skilful, enquiring and a whirlwind of enthusiasm and energy. I like to think John Wilson and I were like that back in the day and Robbie certainly takes me back to my halcyon days. That's not the point. Very recently, Robbie took the most magnificent upper river wild brown trout, on a mayfly pattern. We tend to think of Robbie as a lure maestro but there's nothing this kid can't turn his hand to.

It's been bugging me for a few years why our wild brown trout seem to be coming back to our upper rivers where chub, roach, dace and barbel seem to be struggling. I think I have the answer.

Just a few days ago, I was down on one of the upper rivers, looking out for fish preparing to spawn on the shallows. This is an annual pilgrimage of mine and I find it thrilling to watch our river fish emerging from the depths, beginning their courtships. Over half a mile, I had identified three different gravel, shallow spawning redds, already populated by some good fish of all the above species. I'd been watching in peace and serenity for a few hours before mayhem broke out.

A flotilla of six canoes barged noisily down the stretch of river in question. As the river is still comparatively low, even after the recent rains, they had to get out on several of the more shallow reaches and pull their canoes over the gravel. Of course, the fish fled back downstream into deeper water and safety. This upsurge in upper river canoeing, especially from mid May to mid June when the fish are actively laying their eggs is disastrous.

Trout, as you know, lay their eggs in the late autumn and winter when the river is high, swollen and there are no canoeists about. Our coarse fish species lay their eggs at the very time that these canoeists are out and about doing their damage.

I tried to reason with the canoeists and received the usual responses that I've always received. Some were simply surly and ignored me. A couple began to preach their right to canoe wherever they wanted to. This is complete rubbish.

A few years ago, the matter was settled definitively by David Hart QC's very clear legal advice. The simple matter of the fact is that there is no general Public Right of Navigation (PRN) on English and Welsh non-tidal rivers for canoeists. The only exceptions to this are when the riparian owners of both banks give permission or where there is a long and established use of boating on a particular river for communication or for commerce. Quite clearly as the stretch of river in question was private and no permission had been given, these canoeists, whether they like it or not, were flouting the law.

I'm quite sure that these canoeists, like most of them, are intelligent and thoughtful people. I have no doubt they regard canoeing as their right, as a uniquely beautiful way to enjoy the countryside which they consider theirs. I can sympathise with all this. However, what they are actually doing is destroying the upper river populations of coarse fish for years to come, if not for ever. Canoeists and canoeists governing body simply have to recognise and accept the law as it is, rather than as they would prefer it to be and to recognise the clear legal rights of riparian owners to exclude canoeists if they wish for the good of the rivers and their fish populations.

This is simply a measure of vital conservation, not the act of a killjoy. Many of us, of course, enjoy Blakeney Point, for example, at this time of the year. There is a well-protected colony of nesting terns. I have no doubt some people would love to trample through the dunes there, getting a better view, enjoying the wild, open scenery. They're not allowed to for the good of the birds. This is why the terns flourish and why our upper river coarse fish species are not doing.

Canoeists. Pay heed please. There are many deep, broad tidal and Broadland rivers where canoes do not do harm.

Enjoy those perhaps but leave the thin, vulnerable upper rivers to the fish.