Anderson (1989) estimated that there are approximately 20 000 small water bodies with an area of less than 10 km2 in Africa, compared to nearly 13 million km of rivers and streams, but this is clearly a considerable underestimate. However, there is still a general lack of information on the numbers of small water bodies in the region, their size, chemical status and productivity. Data on their area and capacity should be available for reservoirs, at least, since this is known when they are constructed. Few countries in the region have systematically collected these data, which are often widely scattered and therefore difficult to utilize.
There are, of course, wide variations in the data from each country and some have made more progress in organizing the data that are available. Zimbabwe, for example, has established a GIS system which has enabled the number of reservoirs in the country to be relatively well documented for the first time (Chimowa and Nugent, undated).
Vanden Bossche and Bernacsek (1990) list 23 small lakes plus three lake complexes in the country. They give the areas for 12 of these lakes, which range form 1.4 to 18.9 km2 in size (mean = 5.2 km2). They also list 18 reservoirs; there are no data for 10 of them, but the remaining eight range from 0.2 to 140 km2 in size (mean = 42.9 km2). There are, no doubt, other small water bodies in the country, but nothing can be learnt about them until the civil security situation improves.
Botswana is largely semi-arid to arid, with a flat topography, and has few natural water resources. Exceptions to this are the Okavango River, which discharges into an inland delta in the north of the country, and the Chobe (Kwando) River, which forms the border with Namibia. Lakes associated with these systems include Lake Ngami (maximum area 200 km2) and Lake Liambezi (maximum area 101 km2), both of which dried out completely in the early 1980s. There are two relatively large dams in the eastern part of the country (Gaborone and Shashi) and about 309 smaller dams, with a total area of 790 ha (Nermark et al., 1992).
According to Vanden Bossche and Bernacsek (1990) there are about 100 ha of small reservoirs that could be used for intensive aquaculture, and 50–100 ha of medium-sized ones that could be used for capture fisheries or cage culture. However, they point out that a number of them have been washed away and others have silted up. Another source (ALCOM, 1993) estimates that there are 590 reservoirs, but only 369 are functional because the others have silted up. Of these, 286 are less than 1 ha in area and their total area is estimated to be 424 ha. Several large reservoirs are under construction, or planned, as part of the Lesotho Highlands Water Project, which is primarily intended to supply water to South Africa.
Even more than Tanzania, Malawi is dominated by large natural lakes, especially Lake Malawi which occupies about 24 400 km2, or 25.9% of the country. Other large lakes include Lake Malombe (390 km2), Lake Chilwa (1 000 km2 when full) and Lake Chiuta (200 km2 when full). Little is known about its smaller waters but it has been estimated that in 1994 there were 755 reservoirs, of which 16 were completely silted up. The total area of the remainder was 2 138 ha, their average size was 7.3 ha and the largest measured 150 ha (ALCOM, unpublished data, 1994).
Inland water resources of Mozambique include a part of Lake Malawi (6 400 km2) and parts of Lakes Chilwa and Chiuta. Vanden Bossche and Bernacsek (1990) list seven small lakes: Amaramba (60 km2), Banamana (20 km2), Marangua (63 km2), Neguri (8.4 km2), Nhangela (15.8 km2), Nhangulaze (14.7 km2) and Nhavarre (22.1 km2). There are also some 400 brackishwater coastal lagoons with a total area of over 540 km2. There are four large reservoirs - Cahora Bassa (2 665 km2), Chicamba (120 km2), Massingir (151 km2) and Pequenos Libombos (47 km2) - but there are no data on the number of small reservoirs in the country.
Like Botswana, Namibia is largely arid and has limited inland water resources. Lake Liambezi on the Chobe (Kwando) River - which is shared with Botswana - once supported a productive fishery, but dried out completely in the early 1980s. According to Haight and Ersdal (1994) there are 18 state dams in the country, with an average area of 4.9 km2 when full (with a range of 0.1 to 29.6 km2). There is also an unknown number (10 000 according to some estimates) of farm dams which are mostly used for watering stock and wildlife. Many are highly seasonal and dry up during the dry season. Some reservoirs and canals are associated with the Eastern National Water Carrier, a major scheme to transfer water from the Okavango River in the north to the central regions (Figure 7). This scheme, and others, should increase the amount of water available for fish production.
In the north of the country, the Cuvelai River flows from Angola into area of flat terrain and flooded soils to form oshanas, which are shallow channels with vegetation which fill with water and are occupied by small fish. These are later caught as the oshanas dry out. Van der Waal (1991) estimated that 250 t of fish were taken from seven oshanas over 60 days, and that they are clearly productive systems. However, the environment has changed through the construction of a canal system to direct water to towns and this may affect their productivity.
Vanden Bossche and Bernacsek (1990) list 9 reservoirs, with a total area of 103 km2 (largest = 84 km2) but there are no other data on small water bodies in Swaziland. In addition, a small portion (6 km2) of the Pongolapoort Reservoir, built on the Pongola River in South Africa, extends into the country.
Figure 7. Inter-basin water transfer schemes in Namibia
(From Allanson et al., 1990)
The only natural lakes in the country are a series of about ten coastal lakes along the northeastern coast (effectively the southernmost members of the coastal lake system of Mozambique) and six along the southern coast. Lake St Lucia (328 km2) is the largest of the former, and Swartvlei (11 km2) the largest of the latter. Not all of these lakes are entirely freshwater, since they are connected to the sea. Large numbers of endorheic pans are found in the more arid parts of the country (Figure 8); most of them are ephemeral and some are saline or brackish. Nevertheless, they can support fish populations if supplied with water and some may have potential for the culture of crustaceans such as brine shrimp (Safriel and Bruton, 1984). Numerous reservoirs have been built in all areas of the country (Tables 3 and 4), although they tend to be more sparsely distributed in the more arid areas of the northwest (Figure 9). In contrast to most other countries in the region, their fish yield is primarily accounted for by anglers (see Cochrane, 1987, for example).
Figure 8. Distribution of endorheic pans in southern Africa. Close hatching denotes areas where they exceed 1/km2
(Adapted from Meintjes et al., 1994)
Figure 9. Reservoirs with walls > 5 m high or capacity > 50 000 m3 in South Africa
(Taken from Davies, O'Keeffe and Snaddon, 1994)
Natural lakes cover about 61 500 km2 -6.5% - of the land area of the country, but most of this is accounted for by the Tanzanian portions of three great lakes (Victoria, Tanganyika and Malawi). There are another 32 natural lakes, of which 21 are smaller than 20 km2 and might therefore be counted as small water bodies (Table 7). The country also has numerous reservoirs, which are mostly sited in the northeastern part (Figure 10). Most of them appear to have a capacity of less than 1 × 106 m3 and to be smaller than 40 ha in area (Table 8).
Table 7. Natural lakes in Tanzania, ranked by size, but excluding saline or soda lakes
| Area (km2) | Number |
|---|---|
| < 5 | 9 |
| 5 – 10 | 8 |
| 10 – 20 | 4 |
| 20 – 50 | 5 |
| 50 – 500 | 4 |
| > 500 | 5 |
(From Vanden Bossche and Bernacsek, 1990)
Figure 10. Distribution of reservoirs in Tanzania
(From Bailey, 1966, cited in Vanden Bossche and Bernacsek, 1960)
Table 8. Reservoir numbers in Tanzania, ranked by capacity and by area
| Capacity (× 106 m3) | Number | Area (ha) | Number |
|---|---|---|---|
| 0.005–0.5 | 203 | 0.5–5 | 126 |
| 0.5–2.5 | 29 | 5–20 | 72 |
| 2.5–5.0 | 6 | 20–40 | 23 |
| > 5.0 | 8 | 40–400 | 19 |
| > 400 | 6 | ||
| No data | 490 | 490 | |
| TOTAL | 736 | 736 |
(Data from Balarin, 1985, cited in Vanden Bossche and Bernacsek, 1990)
Zambia has abundant inland fishery resources in the form of large lakes (2 000 km2 of Lake Tanganyika, 2 700 km2 of Lake Mweru, Lake Bangweulu and Lake Mweru wa Ntipa) and floodplains (Barotse, Kafue, Lukanga Swamp and Luapula). Vanden Bossche and Bernacsek (1990) list four smaller lakes (Mwange, Chisi, Beu and Ishiba Ngandu) but give no other data on them. Large reservoirs include the northern half of Lake Kariba, Lake Itezhi Tezhi and the Kafue Gorge Dam. There are many smaller reservoirs, but while a full inventory is not available, it was estimated that in 1968 there were 700 of them in the Southern Province and 197 in the Eastern province (Gopalakrishnan, 1989). Of 41 dams in this province that were surveyed for aquaculture potential, 27% were less than 10 ha in area, 51 % were between 10 and 20 ha, 20% were form 20 to 50 ha, but only one dam was over 50 ha. Surveys carried out in 1992 (Department of Water Affairs) and 1994 (ALCOM) in the Eastern Province found 228 reservoirs, with a total area of 1 180 ha.
Reservoirs are the only small water bodies in the country, which has no natural lakes. The majority of them have capacities of less than 0.1 × 106 m3 (Table 9). They are distributed throughout the country, except for areas in the north, northwest and south of the country where the topography is flat and generally unsuitable for reservoir construction (Figure 11).
Table 9. Reservoirs in Zimbabwe (1), according to capacity (2)
| Capacity (× 106 m3) | Number |
|---|---|
| < 0.1 | 7 838 |
| 0.1–0.5 | 1 480 |
| 0.5–1.0 | 235 |
| > 1.0 | 265 |
| No data | 600 |
| TOTAL | 10 408 |
Notes: 1. Lake Kariba excepted.
2. Reservoirs with
a capacity >1 × 106 m3 are considered “large
dams”.
(From Chimowa and Nugent, undated)
Figure 11. Distribution of dams in Zimbabwe. Points for individual dams overlap in areas where the density is high.
(From Chimowa and Nugent, undated)
