Fly Fishers' Republic

Wandle Restoration Part VI

September 4, 2006

by Theo Pike

book and phone

Getting to know your river

So, you’ve identified a river you’d like to work on. Since we last spoke, you might even have started making your first approaches to some of the people we mentioned last month. Yet now, through some of those conversations, you’re gradually confirming the suspicion that there are actually a lot of people out there who know a lot more about “your” river than you do.

If you’re a reasonably questioning sort of fly-fisher, and you’ve started tracking out your ideas with a burning sense of mission and the strength of ten because your heart is pure, that can come as a shock.

Relax, Galahad. It’s a shock – but it’s a normal, salutary shock. It keeps you lean, agile, and never completely sure of what you’re looking at.

It’s also something that still blindsides me and my own Polaroid visor slits at least once a month, even after several years’ work and warning on the Wandle. So what’s the training regime for keeping an eco-knight errant safely in the saddle… most of the time?

Exercise 1: walking your water in all weathers, wading it, or riding the banks on your trusty steed of a mountain bike. When you’re starting anything, there’s no substitute for personal observation, and I’m constantly amazed at how few river restorers have ever really covered the catchment they’re working on – sometimes years into the project.

Wading all your water at once may not be possible, but you’ll get an unparalleled depth of understanding when you slip into the bottomless hole where you and your cleanup gang have just grappled out a dishwasher. And how many excuses do you really need to jump into your chest waders and go fishing?

Grab your rod – lancewood, bamboo or graphite – and put it all down to ecological immersion…

Exercise 2: taking another, closer look at that map you bought back in July. Now, as you connect the Ordnance Survey’s contour lines to what you’ve just seen at the waterside, you’ll realise how much you’ve already absorbed by osmosis – and how much you can extrapolate.

If you’re in a heavily urban area, is your river scoured and silted by heavy-metal run-off and flash flooding from roads and car-parks? On remote uplands, what’s the acid-rain effect of the conifer plantations wrapped around that feeder burn?

Down in the farmlands, are the cattle-trampled banks dropping silt into your gravels every time it rains? Is your river a shady tunnel, parched by abstraction, with sad remnants of weedbeds clinging to life wherever light still penetrates the boughs? In any landscape, is there a sinister culvert leaking an oily stain of something unidentifiably nasty?

All these connected macro-factors can give you a powerful sense of direction, and tell you what may need to be done, even at this early stage of analysis.

Now move on to Exercise 3: calling technical support on 08708 506 506. As far as I can tell, the proportion of your hard-earned taxes that ends up in the useful budgets of the Environment Agency just keeps on shrinking. But that shouldn’t stop you finding out what they know about your river, and maybe even how you can help them circumvent the lack of free-flowing cash.

Apart from asking your local conservation officers about the improvements they may have made to your river in, say, the course of the last ten years (hint: prepare to be shocked by scale and ambition, and that’s from recent personal experience) you’ll probably get the best overview from two sets of readily-available data.

One, from the ecological appraisal officer in charge of your area, will be your river’s invertebrate counts, compiled as Biological Monitoring Working Party scores (BMWP).

Taken twice in the same year at 3-yearly intervals, these are lists of all the bugs and other invertebrates discovered during a 3-minute kick-sample at one or more points along your river. After scaling them against established standards of tolerance to biological and chemical pollution, they’ll give you a very clear idea of the ecological richness of your water, and point to some of the changes you may need to engineer. Not least, you may also end up inspired to do some rock-turning of your own (detailed instructions to follow), and carrying a few extra patterns next time you’re out for a flick…

And while you’re still on the phone, ask your local fisheries officer for his latest electro-fishing figures too. Belatedly, this is an angle I’m still investigating on the Wandle – and it doesn’t take a genius to work out what fun we’ll have as a result. But there’s a serious aspect too. Yes, it’s back to the map and the riverside again.

With all this data at your fingertips, if you’re so inclined, it’s time for Exercise 4: calculating your river’s carrying capacity, and working out why and where your trout population’s bottlenecks may be occurring. With profuse gratitude to the Wild Trout Trust’s new “Wild Trout Survival Guide”, here’s a summary of what trout need at each of their life-stages, in order to optimise the chances of forming a healthily sustainable population:

Habitat Spawning Fry Parr Adult
Water depth 25 – 60cm 10 – 40cm 10 – 60cm 30cm
Water velocity 25 – 75cm / sec 0 – 30cm / sec 5 – 50cm / secc 10 – 60cm / sec
Substrate 5 – 50mm gravel, with little silt Cobbles, gravel with little silt Cobbles, gravel with little silt Cobbles, gravel, debris
Cover Nearby deep water, undercut bank, boulders or weed Cobbles, debris and rooted plants Abundant bankside / instream cover Abundant bankside / instream cover

The Guide goes on to say that:

“Assuming a deposition rate of 800 eggs from a standard 500g brown trout, even a small area (say 250 square metres) of good quality riffle could potentially hold upwards of 10,000 eggs. Given a hatching success of 25%, then around 2,500 young fry might be expected.

Excellent-quality fry habitat would not be expected to routinely hold more than one fry per square metre. Using this density figure, a total of 2,500 square metres (ie a 250 metre length of 10 metre wide channel) of fry habitat would be required to support this number of fry.”

Whilst you’re wrapping your head round the biological implications of numbers like these, how they might affect the sustainability of your own fishery, and suddenly realising why rivers have traditionally been divided into overlapping trout, grayling and barbel zones… you might also like to try Exercise 5: asking the Wild Trout Trust for a river survey.

On a sliding scale of Orvis-subsidised costs, you should be able to negotiate a visit from the author of the “Guide”, Vaughan Lewis himself, for a day’s insightful stroll along your river. He’s great company on the walk, and what he says will help to provide you with reassurance and a strategy for the future bound up in a full-colour report. He may even give you an autograph copy of his “Guide”.

Whenever you get the chance, try Exercise 6: talking to the locals about your river and its traditions. And while you’re about it, join in a few of the global village conversations on that modern internet equivalent too, just a click away from where you’re scanning this. Sometimes it’s clear that your self-appointed pub or board expert can’t tell a trout from a chub: at others, you may be astounded by the depth of local or international knowledge.

For instance, from various encounters – some of them very fortuitous – I’m starting to suspect that the upper Wandle still provided marginally-viable habitat for (probably stocked) adult trout long after the lower river had been condemned as a sewer, and only really went belly-up when the Butter Hill vinyl factory started colluding with abstraction to turn the last spring water into toxic soup. Low flows are still with us, but the factory has gone, so now we’ve only got deoxygenation and silting gravels to worry about…

Finally, when winter draws in and your river’s thundering down in black, impregnable spate, indulge in Exercise 7: reading all about it. If you haven’t already discovered as the ne plus ultra of the eccentric, the extremely inexpensive and the downright out-of-print – do it now and thank me later.

Knowing about the historic past will help illuminate your river’s path into the future. For instance, when a freshwater biologist friend told me he’d just seen a pair of brown trout spawning in the Wandle, down towards Wandsworth at the end of April, I doubted his sanity only for as long as it took me to remember a rare old book by a rare old Victorian called Alfred Smee.

He it was who built his own trout and char hatchery in his garden in Wallington, but that’s not the point right now: he also recorded how there were two distinct native strains of Wandle trout, one with white flesh and one with red, and how the white-fleshed strain was fit to be caught in May while the red-fleshed trout only came into condition in July or August. Coincidence or truly Damascene flash of truth? I’m still not sure, but remembering old Alfred’s testimony certainly helped me make sense of Felix and his oath-sworn summer spawners.

Only connect. In the business of river restoration, isn’t that what we’re all trying to do?

And don’t all those exercises feel good? Now, repeat as necessary…

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