Lac de Guiers, lying in the far north of the country, c.20 km south-west of Richard-Toll, is the only large freshwater lake in Senegal. It lies in the dry valley of the Ferlo river and is fed only by rainfall or by floodwaters coming down the Senegal river and allowed to flow south into the lake through sluices and a canal at Richard-Toll. The lake is 35 km long and 7.5 km wide at its widest point. At high-water it covers an area of nearly 17,000 ha. It is used as a water-supply for Dakar, as well as for local consumption and to supply water for the sugar refinery at Richard-Toll. It is surrounded by Sahel thorn-bush savanna, used for livestock-rearing and ‘walo’ (flood-recession agriculture) and areas of irrigated cultivation, including extensive sugar-cane plantations and rice-fields. There are permanent herb swamps dominated by Phragmites and Typha along parts of the lake shore and scattered acacias and other trees used for roosting and breeding by a wide variety of colonial nesting herons and egrets.
See Box for key species. The site is particularly important for breeding colonial waterbirds (mixed colonies of herons, egrets, spoonbills and ibises) and for wintering waterbirds, but it has never been surveyed regularly. Only one comprehensive survey of the whole lake has been carried out, in 1991 (Baillon pers. comm.). Phoenicopterus minor is recorded from the site, with a maximum count of 1,170 in 1991, making this the largest concentration in Senegal after Djoudj (Baillon pers. comm.). Prinia fluviatilis was recorded from the site in the 1980s, with no details given except location (Lac de Guiers, 16°25’N 15°45’W) and the interpretation that it is likely that the entire lake region is inhabited. One other threatened species, Aythya nyroca, was recorded frequently, but irregularly, wintering in the lake in the 1960s and 1970s, but there are no more recent records. A higher total than that given in the Box for Platalea leucorodia was recorded for the site and the Ferlo: 440 birds in 1991. In addition to species listed in the Box, the site provides the most easterly records in Senegal for Phoenicopterus ruber (400 in 1991), Philomachus pugnax is regularly recorded in rice-fields adjacent to the lake and a suspected roost was reported just north of the lake in 1992. A total of 155 Sterna nilotica was recorded for the area including the lake in 1990, together with sites SN001 and SN004 (but the majority of these birds on the lake itself). Five of the 12 species of the Sahel biome (A03) that occur in Senegal have been recorded from this site (see Table 2). Numbers of many species will depend very much, from year to year, on water-levels within the lake and in other large water-bodies in the region. Waterbirds are known to move (both within and between seasons) between several sites within the wider Senegal river delta area, including the Djoudj wetlands (site SN001), the Ndiaël basin (SN002), the River Senegal (SN004) and the Diawling National Park in Mauritania. These movements appear to depend on the relative water-levels as well as other factors and, as part of a wider network of fresh and brackish water-bodies, the lake is likely to be important for certain species.
Non-bird biodiversity: The lake contained a resident population of the mammal Trichechus senegalensis (VU) until the mid-1980s, but this population was isolated from animals in the main Senegal river and appeared to be declining. It is probably now extinct.
BirdLife International (2019) Important Bird Areas factsheet: Lac de Guiers. Downloaded from http://www.birdlife.org on 22/01/2019.