A Trout Fishery of your own

6 Minute Read

Written by Mike Swan, GWCT Head of Education. This article first appeared in Shooting Times.


I have seen the scenario many times, a lovely little bubbling brook, with a nice head of small trout, but nothing much over a few ounces in weight. The immediate response for someone who wants to improve the fishing potential is to suggest stocking with some bigger fish. But hang on a moment, if the nature of the stream is that it will only sustain wild trout up to 20 or 25cm long, why would you expect bigger stockies to do well? If the cunning little natives can only just eke out a living, why should big tame fish prosper?

The truth is that stocked trout almost always lose condition from the moment they are put in. Having been selected for their growth potential and fed what amounts to an unlimited supply of pellets, they are programmed to grow faster than nature can generally sustain. Length extension may well carry on, but the body grows slimmer at the same time. This is illustrated especially strongly in early spring, when the odd one that has overwintered gets caught, and turns out to be all head and tail, with a body hardly thicker than an eel. Being thin and weak it gives up without much struggle, and tastes pretty awful if you are daft enough to try. Please don’t think such a fish will recover during the summer – tap it on the head and feed to the mother in law’s cat, before it consumes any more of the river’s production.

Impacts of Stocking

Many larger rivers, and especially chalk streams are stocked, providing excellent fly fishing, a valuable recreational resource, and a strong motivation for good conservation friendly management. I count myself lucky to have had great fun on many different stocked rivers, and when the neighbours are stocking as well, there is no particular reason not to. I have even dabbled in stocking myself, on a small section of a chalk stream near GWCT HQ, but for a small personal fishery I advise thinking twice. To do so legally you will need a permit from the Environment Agency (EA) or its equivalent in your jurisdiction. You may also be less than impressed with the results. I certainly never caught more that about 30% and going catch and release did not improve this; those hatchery fish faded away even if my guests and I did not tap them on the head.

You should also think about the impact of hatchery trout on a shared fishery. Remember when you stock a stream it is not a goldfish bowl. Those fish can move, and many do, going both upstream and down. This is especially so in small spate streams, where floodwater can wash your fish away, potentially to the irritation of your neighbours. More significantly, even small stock trout are predators, eating smaller fish including salmon and trout fry, and probably also competing with the natives for food. So, unless other stretches of the river are already being stocked, I’d advise against it.

Improving the River

This does not mean that bigger fish are out of the question. There is lots that can be done to improve the productivity of a stream, providing more food, and growing bigger fish. Many people think that trees and shade are good, helping to keep the water cool in hot weather. There may be some truth in this, but shading means less in stream vegetation, and that means less food and habitat for the aquatic invertebrates that are the main food for your trout.

If you then throw in free access for livestock, to trample the banks, make the stream wide and shallow, and gobble up waterweed, you end up with a very poor stream and only a few small fish. GWCT research back in the 1990s showed that fencing out livestock had a dramatic effect on the productivity of a stream, with consequent improvement in the size and numbers of fish. Recent results from our fisheries team emphasise this, showing that water buttercup (Ranunculus), which only thrives in streamy water in full sun, feeds more and bigger parr compared to streams without.

Most degraded streams also lack structure, with few or no deeper pools for bigger fish to lurk in. Given time, this will recover to a more natural pool and riffle structure, but it is easy to speed the process with current deflectors jutting out from the bank. These are far easier to build than big dams and weirs, and more effective to boot. They are also no problem for migrating fish to get past.

The key thing to understand with current deflectors is that whenever water crosses a barrier, it sets off at a right angle to it. So, although it may seem counter intuitive, a current deflector should face diagonally upstream, so that water passing over it is directed to join and reinforce the main current past the end. If you then make sure that the deflector slopes down into the river, with the outer end just under water at summer level, you will find that it creates a self-cleaning pool just downstream. An easy way to create a deflector is to cut down a bankside alder, and anchor a section of it in the water, with steel reinforcing rods driven in and fence wire to hold it down.

Current deflectors can be set up on alternate sides of the stream to re-create a natural meander, or they can be used as a pair to pinch the river and make a central pool just downstream. Either way, in the natural order of things, a stream normally makes a pool about once in every five widths, so deflectors should happen at about the same frequency. Please also remember that all such structures act as partial impoundments, and therefore need consent from the EA or equivalent. Being small, low structures, they are much less controversial than bigger weirs, and therefore less likely to be refused.

A Stillwater Fishery

While I am not much for putting trout into small streams, I am much happier to stock a pool or lake, provided there is no significant inflow and outflow stream for fish to escape into. The water must come from somewhere of course, and few pools that are big enough for trout will be reliant on rainfall alone. But it is relatively easy to grid off a spring or ditch fed pond so that stocked fish cannot escape downstream. Meanwhile, with no inflow stream to spawn in, there will be no fry to leak past the grid to the detriment of wild natives down below.

For trout to survive warm summer weather, you will need a fair depth, so that the water stays cool, with most of the area at least eight feet (2.4m) deep. Your pool also needs to be large enough for an oxygenating ripple to form whenever there is a bit of breeze – but then you also need room to cast your fly, so those two factors work together. Room for the backcast also means not too many trees close to the bank, but that means good sunlight for the bankside reeds, rushes and other vegetation so that is good for biodiversity too. You clearly also need decent clean water, with no pollution or run off issues. You can test for quality, but this is rarely a problem, and it may be just as easy to introduce a few fish and see how they do. That said, you still need EA permission to stock, but once granted a licence should be in perpetuity.

In choosing what species, folk have a prejudice for brown trout over rainbows, but I would still choose the latter. As well as being cheaper, rainbows are tougher, and a tad more heat tolerant, so less likely to be troubled by hot dry weather. I dare to suggest that they are also more athletic on the end of your line, and better eating when you tap them on the head. Don’t be temped to lay them on too thickly, 300 per acre may be suggested in the literature, but I would suggest half that as plenty, so that there is more natural food per fish.

Remember that trout are the ultimate competitor with ducklings, clearing nymphs that would otherwise hatch into duckling food long before they reach the surface. That said, a good trout pool has mostly steep sides and not much shallow water for the herons to wade in. This means that it will have limited value for surface feeding ducks like mallard and gadwall anyway. If you have newts, they will likely be gobbled up too, but good amphibian breeding ponds are usually far too small for trout.

Well managed fisheries are a joy to experience, but it does not end there. There is always value to other wildlife too, and a restored trout stream, in particular, is a jewel in the countryside for terrestrial as well as aquatic wildlife.

…the GWCT Fisheries team work hard to undertake leading research in to the declines in salmon and trout populations. You can help them continue their vital work by supporting the GWCT Fisheries team from as little as £3. We are a small charity and every contribution, no matter how big or small, can help make a real difference. It only takes a minute and all cards, Direct Debit, Apple Pay, Google Pay and PayPal are accepted:


Small trout fishery

at 13:20 on 14/09/2021 by Martin Richardson

We built a half acre "trout" lake at our last house in North Yorkshire in a damp area of a field that flooded and may have had a farm pond in the past. Environmentally and recreationally it was really marvelous but the points that Mike Swan makes are right. The trout we stocked were easily caught at the beginning but slowly began to lose condition, even "Big Max" who started life at about 5 lbs. The successes were the waterside plants, the wigeon that came and stayed every winter, mowing my lawn for me, the Greylag geese that came to nest on the island every year, the mass of aquatic insect life and the residents coots and moorhens. The problems were the Nuttall's pondweed that I stupidly introduced at the start from a small garden pond, which spread everywhere and the number of mallard who scoffed the wild bird food as soon as it hit the ground and then weakly I gave in and gave them corn of their own. Overall it was certainly a success but not for trout fishing. The final denouement came one hot summer when the combination of roasting temperatures and removing the Nuttall's pondweed was too much to maintain the oxygen levels in the water. The few remaining trout turned belly up and died. Sad!

Mike Swan's stocking article

at 11:20 on 14/09/2021 by MARK FIRTH

Excellent article Mike. As to stocking still waters, I agree with you re rainbows. We recommend 100lb weight of fish per acre, which sounds similar to your suggestion but perhaps a better guide as it takes account of the desire to stock a couple of 'biggies'. All best Firthy Hooke Springs Trout Farm

Restocking trout

at 11:12 on 14/09/2021 by Adrian Riddle

Mike, (sorry, 2 weeks running), one thing you didn't mention was the devastating impact that otters can make. Interestingly locally, (I'm now near Tiverton), they reckon that the number of signal crayfish has led to the increase in otters. On the Exe where I fish, not only otters and the odd cormorant, but up to 8 gooseanders! There used to be huge shoals of dace, virtually none left! Regards, Adrian

Make a comment

Cookie Policy

Our website uses cookies to provide you with a better online experience. If you continue to use our site without changing your browser settings, we'll assume you are happy to receive cookies. Please read our cookie policy for more information.

Do not show this message again