The Cardiff Reservoirs are important for a whole range of wildlife. They incorporate two Sites of Special Scientific Interest (SSSI) and four separate Sites of Importance for Nature Conservation (SINC). In addition there are a number of other nature conservation sites immediately adjacent to the reservoirs.
Lisvane reservoir was declared an SSSI in 1972 for its birds, in particular the large numbers of overwintering tufted duck and pochard. These numbers have decreased in recent years but they can still be seen in good numbers, particularly in cold weather. It is also a good site to see mallard, coot, mute swan, great crested grebe, little grebe and various species of gulls. Other water birds often drop in, particularly on migration and these include other species of grebe, divers, terns, and occasional waders.
During the winter, the reservoirs are home to many species of water birds. On almost any visit it is possible to see tufted duck, pochard, mallard, coot, moorhen, great crested grebe, little grebe, cormorant, mute swan, black-headed gull, common gull, lesser black-backed gull, and herring gull. Other species that are regularly seen include grey heron, Canada goose, wigeon, teal, shoveler, goldeneye, sparrowhawk, buzzard, greater black-backed gull, tawny owl, kingfisher, green woodpecker, great spotted woodpecker, pied wagtail, fieldfare, redwing, and raven.
Common passage migrants include: common sandpiper, grey wagtails and wheatear. Rarer passage migrants include: osprey, green sandpiper, redshank, greenshank, common tern, arctic tern, and black tern.
In the summer months many species migrate to Britain to breed. In addition to the species listed above the following can be seen on almost any visit: sand martin, swallow, house martin, swift, whitethroat, blackcap, chiffchaff, willow warbler. Many of our commoner resident birds such as the blue tit, great tit, carrion crow, chaffinch, greenfinch, goldfinch etc. also breed in the woods and hedges surrounding the reservoirs.
Fungi and Plants
The grassy slopes on the embankments of both Llanishen and Lisvane reservoir have been found to support significant populations of rare waxcap fungi. Waxcap fungi are important in conservation terms because they are indicators of high quality unimproved grassland habitats. Although waxcap fungi were once common throughout Western Europe, they are very intolerant of chemical fertilisers, and as most of our countryside is now treated with fertilisers to increase yields, they are becoming increasingly rare. Waxcaps like nutrient-poor grasslands, but they also prefer grazed meadows where the grass is short. Obviously the reservoir embankments are not grazed, but the relatively frequent mowing of the grass, required on reservoir safety grounds, has a similar effect to grazing. Twenty-nine species of waxcaps have been found in the grasslands surrounding the reservoir. This is an exceptional diversity and means that the site qualifies as one of international importance for waxcap fungi. In September 2005 the Countryside Council for Wales notified the embankments of both Llanishen and Lisvane reservoirs as a Site of Special Scientific Interest for grassland fungi.
As well as fungi, the reservoir embankments are home to a wide variety of wild flowers that are typical of those found on unimproved grassland habitats such as the hay meadows of earlier times. They include species such as pignut, quaking grass, yarrow, yellow rattle, devil’s bit scabious, common twayblade orchid and common spotted orchid. In fact, five species of orchid have been recorded from the site, and in addition to the above, there is also early purple orchid, green-winged orchid and bee orchid, although the latter two species are uncommon.
Unfortunately, during Western Power’s ownership of the reservoirs from 2005-2013 there was much unauthorised access to the site, especially for dog walking. The combined effect of trampling and the addition of nutrients through dog-fouling led to the grassland on the embankments becoming substantially degraded, and coarser grasses began to dominate. However, since the site passed to Celsa’s ownership and then that of Dŵr Cymru / Welsh Water, the embankments have been better protected and have largely recovered.
The reservoirs support a number of mammal species including otters and badgers. Although these are rarely seen, otter spraints have been regularly found on the Nant Fawr stream, which runs through the site, and there is evidence of badgers foraging on the grasslands of the embankments. The site is also extremely good for bats, and all three species of pipistrelle (common, soprano & Nathusius) have been recorded, as well as noctules, Daubenton’s bat and long-eared bats. Although there have been no systematic surveys of small mammals on the site, field voles can be very common in some years, harvest mice have been recorded from the adjacent meadows and dormice are possibly also present.
Reptiles & Amphibians
There is a large population of common toads which breed in Llanishen reservoir. Palmate newts and common frogs can also be found in the old fishponds in the woods below the main dam. The grasslands surrounding the reservoirs are well-known for supporting a large population of grass-snakes, possibly as a result of the ready availability of their amphibian prey such as toads. Slow-worms have also been recorded using the site, and are often seen on the adjacent allotments.