Wensum Anglers Conservation Association, Lyng, Norfolk.

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The wildlife and environment around the Wensum-ACA fisheries

Compiled by Rob Fuller, Russell Francis & Charles Sayer

One of the great pleasures of fishing the river and lakes at Lyng is the rich wildlife living in the beautiful surroundings. This part of the Wensum valley contains an especially rich mixture of habitats – a river with a complex floodplain containing marshes, dykes and ditches, wet woodland, recently planted woodland and gravel pits of varying maturity. Consequently, a wide range of plants and animals find suitable living conditions in the area and, regardless of the time of year, there is always interesting wildlife to be seen.

Like all parts of the countryside, the central Wensum valley has seen large changes in the twentieth century. At Lyng, gravel has been extracted from the floodplain, in some cases reducing areas of marsh but creating new interesting wetlands. The banks of the more recent gravel pits are rich in orchids and other plants (see below). As the pits mature, scrub and trees colonise supporting a variety of birds. The contrast between Sparham Pools, a Norfolk Wildlife Trust reserve, and the Square Meadow lake complex is striking – each offering a very different set of conditions for birds and other species. However, the river itself forms the central, and arguably most precious, feature of our fisheries.

Wildlife of the river

The Wensum is one of the few UK rivers designated as a Site of Special Scientific Interest, as an example of an enriched, calcareous lowland river, with ‘a total of over 100 species of plants, a rich invertebrate fauna and a relatively natural corridor’. The SSSI citation (available online) makes interesting reading, listing many characteristic and frequently scarce, species of plants and invertebrates. Two of the most notable river species mentioned are White-clawed Crayfish and Brook Lamprey. The native crayfish is almost certainly extinct at Lyng, usurped by the signal crayfish which has spread throughout much of the river since the 1980s. The lamprey, however, appears to be present in reasonable numbers on our sections of the river. A third notable species is the Desmoulin's Whorl Snail which is something of a Broads speciality. Populations of this tiny snail have been greatly reduced by wetland drainage across Europe. The snail lives in permanently wet fens and marshes close to rivers or other water bodies. Although there are populations along the river valley, it is uncertain whether it occurs at Lyng.

Brook lamprey found in sludge during the excavation of a fry refuge at Sayer’s Meadow in 2017.

The native white-clawed crayfish. Now almost certainly extinct at Lyng.

In the 1960s the community of aquatic plants was quite diverse throughout the individual sections of the river, i.e. between mill structures. Immediately downstream of the mills, Perfoliate Pondweed extended for large distances with occasional beds of Water Crowfoot on the more gravelly, shallow sections. As the river gradually slowed Bur-reed became the dominant species with Yellow-Waterlily occurring in the deeper, slow section immediately upstream of the mills. The situation today is that the waterlily now often extends much further upstream of the mills into water far shallower than formerly. Upstream of this, Bur-reed is by far the dominant species with a much-reduced area of Perfoliate Pondweed nearer the mills. Other species are much reduced or largely absent. In fact, at times the Bur-reed itself completely disappears for a number of years on some stretches leaving a largely barren ‘desert’ with no macrophyte cover for large distances.

One of the wonders of the Wensum in the early years was the diversity and abundance of insect life. Various species of caddisflies and Baetis and Ephemera mayflies were extremely common. Indeed, one could watch diurnal swarms of brown/black ‘silverhorn’ caddis appear over hundreds of yards of the river’s length. By the early 1980s, however, all caddis species were noted as only at a fraction of their former numbers. A similar situation exists for the mayfly species, although Ephemera danica still appears in varying numbers. The Freshwater Shrimp was also abundant in former times, with large numbers found clinging to any submerged material. Today, the shrimp is much reduced, if not actually absent in the middle to lower reaches of the river.

Whilst the river and its wildlife are far different than just 50 years ago, with regrettable declines in river plants, invertebrates and, of course, Roach, it remains a wonderful peaceful place to fish. Some of the processes that have driven these changes are described below.

The unstable river environment

Rivers and their floodplains are highly dynamic due to a mixture of natural events and human activities. Like so many English rivers, the Wensum suffered from brutal dredging in the decades following the Second World War. This was merely the most recent episode in a long history of human modification of the river. It is hard to imagine what it must have been like before the many mills were built but these utterly transformed the river with flow rates and patterns of sedimentation being very different above and below the mills. Many of the characteristic plants and animals presumably redistributed themselves into those sections of the modified river that best matched their preferred habitats.

A complex of recent human activities has contributed to the changing the character and behaviour of the river since the mid twentieth century. Dredging, silt removal and annual weed-cutting have declined almost to zero. Privately owned sluices are now generally left fully open all year round and the Authority-controlled (now EA) sluices are subject to some form of automatic regime. Far less tree/shrub removal is carried out than in earlier years, though many stretches have very little tree cover. Crucially, land use within the catchment has altered greatly with, for example, huge increases in application of synthetic fertiliser, a shift from spring to autumn sowing of cereals, and a large expansion of maize crops mainly for biofuels. The human population and, especially, traffic flows within catchment have risen. With an increased range and volume of inputs and pollutants from agriculture, waste water and roads, the quality of the river water inevitably differs to that of 50 years ago.

The average flow has diminished and the river is far narrower in terms of open water. In many places it is easy to see where the river is undergoing a process of active constriction, effectively compensating for the reduction in flow. This has created areas of marshy margins often making access for fishing difficult though this should be a temporary phenomenon as these margins gradually firm up as vegetation consolidates. Following heavy rainfall the river seems to rise more quickly but also rapidly drops back – more so than several decades ago. Summer floods now seem more frequent. Some of this may be due to changing rainfall patterns but land use in the catchment probably contributes.

In recent decades, the river has greatly narrowed in many places due to reduction in flows. This picture, taken at Sparham Hall in 2019, shows a Wensum-ACA member standing on the original river edge with the current channel just visible several metres beyond.

Even in summer at normal levels, the water can sometimes appear rather turbid possibly due to suspended particles and / or algal growth due to nutrient changes. Sedimentation has reached serious levels. Slower stretches and sheltered features such as fry refuges are especially vulnerable to the accumulation of glutinous sediment. However, even in the faster water gravel beds are not immune and require regular desilting. Agriculture – especially poor location of crops such as maize on hill slopes – is a source of much of the sediment but erosion of road margins due to elevated traffic levels also contributes. Sediment is composed not just of soil (soil loss is a really serious issue in itself) but also substances derived from the wear of vehicle tyres for example. Although work has been undertaken to reduce sediment-laden run-off, much remains to be done. Silt traps can be effective though these require regular excavation. But fundamentally, the solution has to be one of preventing the sediment leaving fields and roads wherever possible.

Sludge excavated from a fry refuge in 2017; this gives some idea of the scale of the sediment problem in the modern river.

What can we do to improve the river environment?

The above factors will all have altered, mostly in negative ways, the plant composition and populations of aquatic invertebrates with implications, of course, for habitat quality for fish. The Wensum-ACA is actively involved in working with our riparian landowner and other organisations including Environment Agency and Natural England to improve the environment of our river fisheries. The main ways we are doing this are through:

Creation of fry refuges – these are small offshoots from the river which potentially offer sanctuary for fry and small fish at all times of year, but especially in periods of flood.
Folding back the marginal sediment and vegetation to create occasional ‘mini bays’ which increases habitat diversity in the margins.
Creation of riffles which are important for both spawning and feeding fish – historically this has been a major activity at Sayer’s Meadow with considerable success.
Increasing the amount of coarse woody debris in the river to provide habitat for aquatic invertebrates and cover for fish from predators. This can involve leaving fallen trees, or parts of them, in place or actually inserting dead wood into the river.
Placing ‘flow deflectors’ in the river at locations where the effect is to speed up the current thus increasing habitat diversity and / or scouring gravel to reduce sediment.
Tree planting at the river edge can help to increase terrestrial insects, many of which will find their way into the river and be eaten by fish. Overhanging trees often offer important cover for fish (and nice swims for fishing). We have mainly used alders but a small number of the rare black poplar have been planted too.

A flow deflector at Sayer’s Meadow; this was installed in 2019.

Beyond the river

Over recent decades, a remarkable wealth of wildlife has been recorded for the farm within which our fisheries are situated. Some of the most interesting aspects are summarised here, starting with the plants.

Plants

There is an impressive plant list of 450 species. It is a site of particular importance for arable flora on acid soils. This status has been achieved through sympathetic management coupled with visits from the experts of the Norfolk Flora Group who can identify plants you didn’t know existed! Both on the managed farmland, and around the lakes, the flora is ever changing. Some of the ephemeral plants that appeared when the lakes were being worked have already disappeared. However, about 150 species can be found in the immediate vicinity of the lakes and the adjacent new plantation. In 2018, five species of orchids were in flower at the same time: Twayblade, Southern Marsh, Early Marsh, Common Spotted and Bee Orchid. The lake edges can be covered with the attractive Bog Pimpernel, and Meadow Saxifrage appears in some years.

Frogbit in a fry refuge at Sayer’s Meadow in June 2019. This free-floating plant is locally distributed and declining. It occurs in slow-flowing calcareous or base-rich water.

Bog Pimpernel next to one of the gravel pits at Lyng.

Marsh orchids growing by a gravel pit close to Square Meadow car park.

A less desirable species that has strongly colonised the shallow margins of the lakes is New Zealand Pygmyweed. This non-native plant smothers native vegetation both under the water and on the adjacent bank. Anglers should be aware just how easily it is transferred from one water to another – just a tiny fragment of weed on wet boots or nets could be enough to establish the plant at a new lake.

A dense mat of the highly invasive New Zealand Pygmyweed. It typically forms dense mats in shallow water at the margins of ponds and lakes and will smother both aquatic and terrestrial vegetation. This photo was taken close to Square Meadow car park. There is a risk that anglers could easily spread the plant to other water bodies.

Invertebrates

A total of 21 species of damselflies and dragonflies have been recorded. Around the lakes Common Blue, Blue tailed, and Large Red-eyed Damselflies can be abundant. There are lesser numbers of Azure, Large Red, and Small Red-eyed Damselfies. The Willow Emerald arrived for the first time in 2018. Banded Demoiselles are commonly seen where there is tall vegetation along the river bank. Hairy Hawker is normally the first dragonfly to appear. Four-spotted Chasers come soon afterwards and are very common, while the Broad-bodied Chaser is rather scarce. Emperors are common and Norfolk Hawker was another newcomer in 2018. Black-tailed Skimmers are frequently flushed from the tracks, and later in the year Brown, Southern and Migrant Hawkers appear with Common Darters.

Pretty much every year, 23 species of butterflies occur on the farm. Green Hairstreaks, Small Copper, Holly Blue, Common Blue and Brown Argus are notable around the fishing lakes and Purple Hairstreaks frequent the oak canopy. From time to time White Admirals and Silver-washed Fritillary occur in the woodlands. To encourage them, work in the woods is carried out to allow sunlight to filter in to the rides and clearings. This year (2019) Charles was excited to find two Silver-washed Fritillaries in a new ride managed specifically for butterflies. It’s always so rewarding when habitat management for wildlife works. Clouded Yellows turn up most years now and are usually seen on the field by the cattle sheds. In all, 33 species have been recorded, but two of these have disappeared – Small Heath and Wall Brown.

Silver washed Fritillary.

The wide range of flora provides for the requirements of many moths, both as a nectar source for adults, and food source for larvae. ‘Get the food-plant, get the moth’ as one of Charles’ mothing contacts once said: and it neatly encapsulates the importance of biodiversity. An astonishing 840 species have been recorded here to date. They range from the showy hawkmoths to less spectacular Wainscots. They have brilliant names such as Uncertain, July Highflyer, Setacious Hebrew Character, Drinker, Old Lady and Scorched Carpet. There is something there for everyone: they look terrific too, as well as being important pollinators, and providing food for bats!

Bats

Recently there has been growing interest in the status and natural history of bats, partly enabled by the use of bat detectors that convert the ultrasound echolocation signals of bats into audible frequencies. At Sparham studies of bats have been carried in two main ways. (1) Participation in the BTO’s bat recording scheme has been going on here for four years. This is in the form of static detectors which are left overnight at three sites on two different nights. Every time a bat passes over, its signature is recorded. Separation of some similar species can be tricky, and when the data are sent away for analysis, some species are ‘lumped’ together. However, the following have been positively identified: Common Pipistrelle, Nathusius’ Pipistrelle, Soprano Pipistrelle, Noctule, Natterer’s, Daubenton’s, Brandt’s, Whiskered, Leisler’s, Serotine, Barbastelle, Brown Long-eared. And that is pretty much a full set of Norfolk’s bat species. (2) A bat group has conducted bat ringing with mist nets for the last two years. On an average netting session they get between 10 and 20 bats. At the Sparham lakes, where there is a sheltered wooded corridor, they have caught 100+ on two occasions and had to close the nets as they were unable to process them quickly enough. Which proves that before they came to Sparham, the bat group were netting in the wrong place! But more seriously, that the Wensum valley is a really important wildlife corridor.

Birds

Many anglers take a special interest in the birdlife of the Wensum-ACA fisheries. Not surprisingly, with such a high diversity of habitats, the area is rich in birds. The bird list stands at about 210. In an average year Charles sees about 120 species on the farm. Some of these are in decline or have disappeared. However, there are newcomers such as Little Egret and Great White Egret, and many more raptors than years ago. Ospreys quite often appear on passage, mostly in the autumn. Charles has now seen over 50 here – which is about one a year since his first in 1968 with a maximum of five in a single year. Around the lakes and river, Kingfisher, Bittern, Water Rail are all regular, together with a wide variety of other waterfowl and breeding Common Terns. Black Terns appear most springs on passage. Waders pass through but seldom call in now that the lake fringes are well vegetated. During gravel extraction, however, nearly all the regular passage migrant waders seen in Norfolk were noted. Rarities drop in occasionally, for example Ring-necked Duck and Purple Heron in the last six years. The valley provides nesting opportunities for many summer migrants, and on a good spring day nine species of warbler can be heard. The arable land with its enhanced margins and winter bird food, hosts good numbers of Skylarks, Linnets, Yellowhammers and Reed Buntings, all of which have seen declines elsewhere.

A final thought

Anglers spend such long periods of time (though never quite long enough of course!) at the edge of the water that they are in an excellent position to make valuable wildlife observations. Dragonflies and birds are obvious candidates – many anglers are knowledgeable about these. Other groups where anglers are well-placed to make observations include the emergence of river flies. Wensum-ACA is always keen to hear about any exciting observations (for example on our Facebook page) and to receive wildlife photographs that could be suitable for the website.

An early morning misty view of one of the gravel pits with a Great Crested Grebe fishing in the middle distance.