Rivers and Streams

In their natural state rivers are dynamic systems, continually changing their course but today few rivers in the UK remain unchanged by humans. Land drainage, flood defences, canalisation, impoundments and adjacent land-use change have contributed to changes in the frequency, magnitude and seasonal patterns of flooding, whilst regulation of the flow of rivers has changed the amount and the way sediment is carried downstream. The removal of bankside tree cover not only results in a loss of habitat, but often increases bank erosion. The use of rivers to dispose of sewage and industrial effluents, together with diffuse pollution from land run-off, can lead to nutrient enrichment of surface waters. This not only impacts upon the watercourse itself, but also can have detrimental effects on any floodplain habitat that still retains some connection with the main stream. Despite this, rivers remain a very valuable biodiversity habitat, with the majority of rivers in Carmarthenshire classified as of good or very good in terms of their chemical and biological quality.

The variety of habitat features found in rivers and streams supports a diverse range of plants and animals; riffles, runs and pools support aquatic species, exposed river sediments such as shingle beds and sand bars are important for a range of invertebrates, notably ground beetles, spiders and craneflies. Sand martins nest in exposed banks and little ringed plover nest on the shingle bars, whilst marginal and bankside vegetation sustain an array of fauna and flora. Rivers and streams can often provide a wildlife corridor link between fragmented habitats in intensively farmed areas and support a range of priority BAP species including otter, water vole, shad, and freshwater pearl mussel.

Current Status in Carmarthenshire

The county has a rich and intricate network of rivers, streams and issues, ranging from narrow, deeply incised upland streams to the more gentle lowland meandering sections of the river Tywi. These are an important part of the biodiversity of the county. This range of river habitats supports a characteristic riparian flora and fauna, and the network of watercourses acts as a corridor for wildlife movement throughout the county, linking wetland sites and bringing wildlife into the heart of our urban centres. The wildlife value of the county’s rivers is recognised on a European and National level through the designation of the Tywi and Teifi, together with the Taf, Gwendraeth and Loughor estuaries, as SSSIs and cSACs.

Carmarthenshire’s main rivers flow south-westwards, from the high ground in the north east towards the coastal lowlands. The longest river in the county is the Tywi (the Teifi is the longer river, but does not run wholly through the county). The Tywi rises on the southern edge of the Cambrian Mountains and flows diagonally across the county to meet the sea south of Carmarthen as one of the three rivers that enter Carmarthen Bay there – the two others being the Taf and Gwendraeth. Other important rivers include the Loughor and Teifi, which make up the boundaries of the county to the south east and north, respectively.

The Tywi, together with its tributary the Cothi, and the Teifi, are famous as salmon and trout rivers, with the Tywi recognised as the premier sea trout river in England and Wales, providing vital commercial income to the local area. The rivers of the coalfield area by contrast, have suffered from pollution for many years but the subsequent recovery of these rivers and streams is one of the great environmental successes of the last two decades. The decline in heavy industry and the introduction of stronger legislation has directly resulted in the cleaning of the rivers and the return of their associated flora and fauna.

The streams of the upland valleys are important spawning and nursery areas for salmon and sea trout, which use the boulder-strewn riffle–pool stretches for food and cover.

In contrast to the fast flowing upland streams are the lowland drainage ditches on the coastal flats of Carmarthenshire. These drainage ditches or ‘pills’ (‘reens’) are found in the Kidwelly–Llanelli–Bynea and Pendine–Laugharne area. They are important for a range of wildlife including the increasingly threatened water vole and invertebrate and bird species. These man-made ditches (dating from early nineteenth century land reclamation) hold an array of distinctive wildlife and they traverse another BAP habitat – coastal grazing marsh. The semi-urbanised ‘flats’ south-east of Llanelli are a major stronghold for the water vole and, like the ditches of the lower Gwendraeth and between Pendine and Laugharne, are home to an assemblage of floating water plants such as frogbit, pondweeds and various bank-side emergents. These plants provide food and shelter for water voles and are dependent on a cycle of maintenance to prevent the ditches becoming overgrown. Various dragonflies – such as the scarce hairy dragonfly, a suite of attractive soldier-flies and passing kingfishers also share this habitat.

The Carmarthenshire Rivers Trust has been formed to work in partnership on projects in on our rivers and river corridors, working with volunteers and local communities.
Current factors affecting the habitat

• Although much reduced, pollution from agricultural, industrial, road and urban sources is still an ongoing concern for riparian ecology. The inappropriate disposal of sheep dip chemicals is a major cause for concern as they are highly toxic to river invertebrate communities even in minute quantities.
• Acidification in the upper reaches of the Tywi catchment limits fish and invertebrate communities and has a knock-on effect to predators such as otter and dipper.
• New road developments threaten to further disrupt the wildlife corridor function of a number of rivers and streams, unless designed with sensitivity and mitigation.
• Hard engineering bank protection schemes (blockstones, gabions) are often environmentally sterile. Opportunities to enhance the environment may be lost or discouraged without proper consideration of biodiversity issues.
• Habitat loss through culverting and infilling of small valley-side streams and issues.
• Gravel removal operations and unconsented in-channel works have the potential for environmental damage and channel destabilisation. It should be noted however that the natural processes of erosion can have biodiversity and landscape gains, e.g. sandbars, sand martin cliffs, although on some larger rivers excessive erosion can be a problem.
• River management systems (e.g. seasonal abstraction, releases of impounded water and abstraction for industry and drinking water) can have deleterious impacts on ecosystems and breeding cycles.
• Livestock trampling and disturbance can damage riverbank habitat, resulting in increased bank erosion and sediment generation, and a lack of tree regeneration and of fencing compounds the problem.
• A fungal disease of alder Phytophthora, is killing large numbers of alder trees throughout the area. This has the potential to lead to increased bank erosion, loss of cover for riparian animals, and major landscape impacts.
• Excessive shading, particularly of smaller watercourses, may diminish biodiversity due to lower water temperatures, light for photosynthesis and perhaps excessive leaves, especially conifer needles, entering watercourses.
• Invasive species, Japanese knotweed and Himalayan balsam are a serious problem along some sections of the river system.
• Game-fishery management has the potential to impact on riparian trees (pruning of overhanging vegetation) and river fauna (regular stocking with fish from non-native genetic stock).
• Amenity – canoeing can, if undertaken without regard to the riparian habitat, have a detrimental effect on the environment.

Aquifer Fed Fluctuating Water Bodies

Aquifer-fed naturally fluctuating water bodies are temporary lakes, called turloughs and found in areas of carboniferous limestone. Turloughs have no visible inlet or outlet streams but are fed from groundwater. They are unique environments both in terms of the geology and the rare wildlife which they support. As they are fed from groundwater they regularly fill with water in winter and empty in the summer. In Carmarthenshire Pant-y-Llyn turlough can be found at the eastern end of Carmel Woods SAC and is the only example of a turlough in Wales. It is usually empty by June–July and fills again from October to December.

Because of the periodic filling with water vegetation is zoned around the turlough specialist plants can be found here that can live with variations in flooding. There is a clear sequence of moss, swamp plants and woody plant communities, which occupy different zones in the basin.

The turlough may not look that dramatic, despite its uniqueness in the country, but it is the habitat of a number of rare and highly specialised species.  A minute species of moss has been identified there called Ephemerum hibernicum, which was confirmed at the time as the first non-Irish record of this species.  It has subsequently been found by a reservoir in Monmouthshire and a lake in Portugal, but is otherwise restricted to a few sites in Ireland.  It needs fluctuating water levels and lime-rich mud on which to grow, making Pant-y-llyn an ideal site for it.  Despite its tiny size, there is little doubt that E. hibernicum is an extremely rare species - probably one of the rarest in Carmarthenshire. 

The lake also holds one of three known Carmarthenshire populations of Aphanorrhegma (Physcomitrella) patens.  This is another small, subtle moss that appears in late summer on neutral or lime-rich ground that has been flooded earlier in the season.  It grows and produces spores in a matter of weeks, which has made it a perfect experimental organism for scientists.  As a result, Aphanorrhegma is the most intensively studied of all moss species.  A few plants from the Pant-y-llyn population were collected in 2005 and are being grown by scientists from Leeds University, who are studying DNA variation within the species.

The other bryophyte of interest at Pant-y-llyn is the large aquatic moss Fontinalis antipyretica, which grows in great hanging masses from overhanging trees that are flooded in winter but exposed in summer.  Fontinalis is a common moss on Carmarthenshire's rivers, but is known from very few lakes in the county.  Its habit of hanging from tree branches is also characteristic of turloughs in Ireland.

There is also a good range in aquatic invertebrates, including aquatic beetles and freshwater crustacean.

The turlough is surveyed and monitored by CCW. The site’s uniqueness makes it very important that its characteristic ecology and hydrology is maintained.

Current factors affecting the habitat

In the past Pant-y-llyn has been threatened by nearby quarrying activities but has been protected by inclusion in the National Nature Reserve. Today it remains vulnerable to actions that may alter the hydrology or water quality.

Mesotrophic Lakes

Mesotrophic lakes (i.e. those in the middle of the trophic [nutrient] range) are relatively infrequent in the UK and largely confined to the margins of upland areas in the north and west. They are characterised by having a narrow range of nutrients, the main indicative ones being inorganic nitrogen (N) and total phosphorus (P).

In Carmarthenshire the following waterbody would classify as mesotrophic: Talley Lakes.

Oligotrophic and Dystrophic Lakes

Oligotrophic and dystrophic lakes are water bodies mainly more than 2 ha in size, which are characterised by their low nutrient levels and low productivity. Oligotrophic lakes usually have very clear water, whilst some examples with dystrophic characteristics have peat-stained waters and occur throughout the UK, but mostly in upland areas of the north and west on catchments with hard, acid rocks. This habitat type encompasses a wide range of size and depth, and includes the largest and deepest water bodies in the UK. Good examples may support some of the least disturbed aquatic assemblages in the UK.

A number of our larger waterbodies have been designated as SSSIs. Talley Lake (SN631337), Llyn Pencarreg (SN537456) and Llyn Llech Owain (SN568151) are all SSSIs, the latter two examples of nutrient poor (oligotrophic) water bodies. Other examples of larger waterbodies in the county include: Taliaris lake (SN633328) and Lliedi Reservoirs (SN511044).

Ponds

The county is not renowned for its ponds and many of the larger examples have been created as a result of industry, e.g. Machynys Ponds in Llanelli created as a result of digging out clay for bricks in the nineteenth century. Bishops Pond at Abergwili is one of the best examples of open water in the county – it is a cut off ox-bow lake from the river Tywi. Some of our ponds have recreational value and are stocked with fish, e.g. Cwm-yr-Oernant ponds at Carmarthen and Old Castle pond in Llanelli. The Wildlife and Wetlands Trust at Penclacwydd have created a number of waterbodies that have soon become high values habitats for biodiversity. Ponds are not a major feature of Carmarthenshire. The NT’s Dinefwr Park shallow, species-rich floodplain oxbow lakes have been proposed as potential ‘Flagship ponds’ under a scheme by the Pond Conservation Trust as they have regionally uncommon species.

An inventory of ponds, including many high-quality sites, has been established as part of the National Pond Monitoring Network and work is in progress to add further known sites to this database. This is publicly accessible (for non-sensitive sites/species) at www.pondnetwork.org.uk.

Current factors affecting pond and lake habitats

• Nutrient enrichment
• Increased erosion and sediment decomposition
• Acidification
• Invasive species
• Infilling (ponds)