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Report No 678-F-001
METSI CONSULTANTS: SUMMARY OF MAIN FINDINGS FOR PHASE 1 DEVELOPMENT
deposits rather than on rocks and would be less accessible as food than those that are lost, therefore there would
be a substantial decline in animal food available for fish and birds.
Predicted shifts in the community composition of the aquatic invertebrates in these reaches are indicative of
strongly deteriorating river health. Conditions of slower flows and higher nutrient and algal levels, suited for
colonisation of disease-vector snails (carrying liver fluke), would be enhanced. Blackflies, Simulium damnosum
which attacks man, cattle and poultry, would increase in abundance downstream of Mohale Dam, and Simulium
nigritarse, which is a bloodsucker, preying on poultry, are expected to increase, particularly in the Paray area and
downstream of Mohale Dam.
The native and exotic fishes of the system are expected to be critically affected in Reaches 2, 3 and 7. The
physical presence of the weir in Reach 1 (Matsoku River) is also expected to affect the native fishes, in particular
the highly threatened Maluti Minnow, as well as trout, which would be threatened downstream of the weir, and
may in time disappear entirely. Additionally, trout, large-mouth and small-mouth yellowfish, and rock catfish would
become rare or absent from Reaches 2 and 3. Where relevant in terms of their present distributions, they would
also be moderately to severely reduced in numbers in Reaches 7 and 8. Orange River mudfish are expected to
show a concomitant increase in abundance, particularly in Reach 2 (40-100% or more), and negligible to
moderate in the remaining reaches where they occur.
It is expected that changes in the amphibians would be manifested as species shifts, with a decrease in the
abundance of the Rana group and increases in the Xenopus group. Although more species would decline than
increase in numbers, it is not clear if overall numbers would change to the point that availability of bait would be
affected.
A loss of water-dependent bird life along the Reaches 2, 3 and 7 is anticipated, largely due to the loss of fish.
African black duck, giant kingfisher and hammerkop, all used for meat or medicine, are expected to show
moderate to severe declines in abundance, as are darters, black-headed herons, three-banded plovers and
white-breasted cormorants, which have no social significance. Conversely, increases in some small mammals,
viz. multimammate mouse, red musk shrew and striped mouse, sometimes possibly to pest proportions, are
predicted.
In summary, the loss of resistance and resilience within the system is expected to be clearly apparent (Table 6.2)
in the reaches proximal to the dams (viz. Reaches 1, 2, 3 and 7), and the loss of river resources to riparian
people, and deterioration in the general health of the river, substantial. The capacity to dilute and transport all
pollutants, including faecal contaminants is also expected to decline. The potentially negative consequences of
drinking river water would thus increase sharply. The potential for future development of the catchment areas or
the remaining water and other resources in the rivers would be compromised as additional disturbance of the
rivers or catchments are expected to result in further declines in river condition. Without the construction of
Mashai Dam (Phase 2), however, the impacts of the Phase 1 impoundments are expected to be considerably
ameliorated by large downstream tributaries.
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