Just as you suggested, I got down the river to photograph the weed I was talking about. I arrived at 1pm and stayed until 5.30pm and this is the timeline of an extraordinary experience as near chronologically accurate as makes no difference...

1pm: I arrive and it’s very hot, bright and the river is passably clear. It’s important for you to know exactly where I was. Remember when we fly fished the shallows with Enoka a while back and met the owner and his horse and trap? Well, I start there and finish my river examination half a mile further up on those gravels where we filmed your program last autumn and I did my limp piece to camera. You’ve never seen the 700 to 800 yards of river between those points though. There the river divides and the main flow runs our side of a long island. The banks are too steep for safe access and the water force is volcanic... way faster than anywhere else along the river I know of.

1.15pm: I leave the bottom shallows where we fished that time with Enoka and spend the best part of an hour watching the river where I have just described. Not just watching but REALLY watching. Polaroids. Binoculars. Mega attention. Examining every stone on the bottom. Moving at snail’s pace, disguising my shadow and becoming as one with the water. I see nothing at first and then a long pale rock moves! Yes. A fish. At first I think barbel, of course, but I look and look and blow me, SALMON. A fresh looking fish of 10lb or so. But there are more of them! Along that quarter-mile run of pelting water I count another SEVEN salmon, one close to 20lb! Extraordinary, I know, almost unbelievable in this day and age, but there you are. I see them and can only think they were in that wild water for oxygen and sanctuary both.

2pm: Now I am up on the rapids at the tail of the pool where we filmed. The weed I was talking about is still there, along a 150-yard stretch of gravel. The river is quick as you know and around 2-3 feet deep, four feet in places. I count at least 100 luxuriant patches of the stuff, but it isn’t ranunculus. It looks more like a freshwater eel grass to me and I decide to take a few strands for proper identification when I leave. The important thing is that weed is here in some profusion and turning the river a pleasing tinge of green. The shelter it provides seems to be doing the trick. There are a few barbel and chub clustered there, presumably with spawning in mind. After all, how much more perfect could it be? Gravel, weed, oxygenated water... paradise. There is even a kingfisher nest on the steep bank behind with the adults winging in and out on a regular basis of blurred blue.

Norwich Evening News: An extremely rare shot of a sea lamprey... complete with JB’s shadow!An extremely rare shot of a sea lamprey... complete with JB’s shadow! (Image: John Bailey)

2.35pm: I see IT! A sea lamprey about a metre long, swirling in the current and excavating one of those huge nests in the gravel where they lay their eggs. I watch it, fascinated, for 20 minutes, its mouth clamped to stones and bricks as it digs deeper and deeper. I even get a photograph of it as it swirls past my legs, pretty unafraid as I‘m standing stock still in awe! It’s not much of an image as it’s got my shadow all over it but it’s proof!

3pm: A commotion in the camp site opposite that I thought was closed until June.

3.10pm: Forty or so kids, between 12 and 14 I’d guess, attack the river with canoes, boards, rubber rings, plastic footballs and the unquenchable energy of youth. They are from Bristol, I’m told, on a trip as school has broken up early and this is the start of half term. I’m forced from the river by the mayhem and sit on the bank, attracting strange looks but making note of the carnage.

4.45pm: An adult, presumably a teacher, announces tea time, and the river is abandoned within five minutes.

4.55pm: I go back to where I was before the rumpus. Every strand of weed is gone, not even the roots remain. My intention to take a plant home for further analysis is thwarted. The sea lamprey is gone too and the nest, so lovingly crafted, has been kicked to oblivion. There’s no sign at all of the barbel and chub and even more tragic, the mud bank containing the kingfisher nest has been used as a slide and has collapsed as a result.

5.15pm: I walk downstream to check on the salmon but the water now is far too muddied to see even six inches into the water. The kids didn’t frolic along their patch so the fish might be there... if I can bear it I might go back soon to check.

5.45pm: I’m home and too dejected to call you. Someone far wiser than me said something like, “forgive them. They know not what they do”. Which is, of course, correct, but what is the point of making a river an SSSI if there is no protection and above all, no education. Somehow, Guv, we have to make people understand that recreational damage in this country is crippling swathes of our environment that we are supposedly sworn to protect. Yes, let kids be kids, but not where near-extinct sea lampreys need their own sanctuary. In the UK we fancy ourselves as being environmentally aware. It’s time we blooming well started proving that.