This paper gives an overview of the main challenges and achievements faced by Windhoek's water management sector. The paper highlights pertinent issues arising from increased water demand, and also explores current and future water supply augmentation options. Water planners experience management challenges as a result of a combination of factors, mainly, lack of funds and staff, limited expertise, poor communication between stakeholders, and weak regulation and enforcement. In order to meet these challenges water managers need to develop more robust and resilient strategies, including greater focus on water demand management.

In the Otjozondjupa Region, Namibia, water is transferred from Swakoppoort and Omatako Dams into Von Bach Dam to limit evaporation losses and bring water closer to the purification plant. There is a gap in the knowledge about the effects on water quality in Von Bach Dam due to water transfer from Swakoppoort and Omatako Dams, as previous studies on such aspects in the area do not exist. The

Toxic phytoplankton in the aquatic ecosystems are dynamic, affecting water quality. It remains unclear as to how possible toxic phytoplankton assemblages vary vertically and temporally in Swakoppoort and Von Bach dams, located in a dry subtropical desert region in central Namibia. The following variables were analyzed: pH, Secchi depths, turbidity, water temperature, total phosphorus, orthophosphate, chlorophyll-a, phytoplankton cells, and water depths. Cyanobacteria dominated the phytoplankton community in the autumn, winter and spring (dry) and summer (wet) seasons, at all the depth ranges in both dams. Microcystis dominated the vertical and temporal dynamics, followed by Dolichospermum. In the dry seasons, higher cyanobacteria cell numbers were observed in comparison to the rainy season in both dams. Spring blooms of cyanobacteria were evident in the Von Bach Dam while autumn and spring cyanobacteria blooms were observed in the Swakoppoort Dam. In the Swakoppoort Dam, the preferable depth ranges for toxic cyanobacteria species were at 5 to 10 m while in the Von Bach Dam at 0 to 5 m range. The findings of the current study indicate that the traditional selective withdrawal of water in the two dams should be performed with vertical and temporal dynamics of possible toxic cyanobacteria accounted for to aid the abstraction of water with the lowest possible toxic phytoplankton numbers, which could lower the public health risk.

No abstract

Ecological restorations of reservoirs are implemented worldwide; however, minimal successes are reported and understood for warmer African lakes like Swakoppoort Dam, Namibia. The objectives of the study were (a) to establish the effectiveness of the two control measures in reducing cyanobacteria growths in comparison with untreated control areas and (b) to compare the results generated before and after control measures with the reference Von Bach Dam. During Phoslock ® treatment, the average cyanobacteria cells and total phosphate (TP) were 90,521 cells/ml and 0.3 mg/L in the treated area and 55,338 cells/ml and 0.1 mg/L in the control area. During Solar Powered Circulation (SPC) treatment, the average cyanobacteria cells were on average 906,420 cells/ml in the treated areas and 121,891 cells/ml in the control area. The TP on average was 0.3 mg/L during SPC treatment, while during the combined treatment, the average cyanobacteria cells, TP, and total nitrogen (TN) were 18,387,226 cells/ml, 0.27 mg/L, and 2.41 mg/L before and 22,836,511 cells/ml, 0.42 mg/L, and 1.50 mg/L after treatment. This was higher compared to the reference site. PCA triplot indicates no grouping pattern, and the repeated-measures mixed model analyses indicate that treatment had no significant effect on cyanobacteria cells. It was evident that the two control measures were ineffective in reducing cyanobacterial cells.Practitioner points:• Key findings of the article:• Two phytoplankton control measures were found ineffective to reduce the cyanobacterial cell numbers. • High cell numbers of cyanobacteria were recorded at the treatment areas compared to untreated control areas during both treatments.• The combined effect of the two control measures was ineffective as more cyanobacterial cells were recorded during the treatment.• During control measure treatment, the Swakoppoort Dam was hypertrophic, which could be due to a malfunctioned WWTP upstream.• The inefficiency of the control measures could be due to small treatment area, higher nutrients, or treatment period.