The Steenbras Dam above Gordon’s Bay is the oldest major dam in Cape Town’s water system and the only one that doubles as a power station. Two reservoirs, one river, and a century of infrastructure holding part of the city together.
In August 2026, Steenbras Upper sits at 99.2% and Steenbras Lower at 53.9%. Those two numbers tell different stories. Upper is essentially full, held there partly because the City needs the hydraulic head to run a power station. Lower is well below its partner, taking more of the draw for gravity-fed supply to the southern suburbs.
Together, the two reservoirs hold about 65,000 megalitres when full. That sounds substantial until you put it next to Theewaterskloof, which holds roughly 480,000 Ml on its own. The Steenbras pair contributes around 7.5% of the Western Cape Water Supply System’s total storage — not the largest share, but a useful one.
A dam built because the city was thirsty in 1918
Seven Cape Town municipalities amalgamated in 1913 to form a single city. One of the first things the new entity had to sort out was water, because the older, smaller reservoirs on the slopes of Table Mountain were already running short.
In 1916, a Board of Engineers proposed a dam on the Steenbras River in the Hottentots-Holland mountains, about 64 kilometres southeast of the CBD. Ratepayers voted on it. The alternative was the Wemmershoek catchment, which would be built three decades later anyway, but in 1918 the money and the referendum went to Steenbras.
Work began in 1918 and the dam opened in 1921. That original structure was modest — a masonry wall that was a fraction of what stands today. The wall was raised twice, in 1928 and again around 1954, as the city grew faster than anyone had planned for. The current concrete arch-gravity wall is 28 metres high and 412 metres long, impounding the reservoir over a surface area of 380 hectares.
Steenbras Lower Dam: gravity is the point
The Lower Dam feeds water to a chain of reservoirs that still carries the city: Molteno in Oranjezicht, Newlands, Wynberg, and further east to Strand and Somerset West. The pipeline connecting it to Molteno is 64 kilometres of cast iron, and parts of it are original, laid in the 1920s and still in service.
The reason the Steenbras site was worth the cost is elevation. The dams sit high in the Hottentots-Holland range. Water flows downhill to the city under gravity, with no pumping required along most of the route. That made 1920s Steenbras cheap to run and makes 2026 Steenbras cheap to run, which matters when the City is balancing operating costs across a system that serves around four million people.
At 53.9% as of early August 2026, Steenbras Lower is well above the critical floor. The combined Western Cape system sits at 78.1%, slightly below the same week last year (84.8%), but still comfortably above the 13.5% operational threshold that defined Day Zero in 2018.
Steenbras Upper Dam: water supply and power station
The Upper Dam came fifty-six years later and runs a power station, something no other Cape Town reservoir does.
Built in 1977, the earth-fill Upper Dam sits upstream of the Lower, impounding 31,767 Ml behind a 940-metre wall. The bigger engineering story is what happens to the water between the upper reservoir and a small lower reservoir on the mountain slope below it.
Water released from the Upper Dam falls about 275 metres through tunnels to drive four 45-megawatt turbines at the Steenbras Power Station, commissioned in 1979. Total capacity: 180 MW. The station is a pumped-storage scheme, meaning it can run in reverse, pumping water back up during periods of low electricity demand, then releasing it again at peak demand. Cape Town owns and operates the plant through its Electricity Department.
At 99.2% full, the Upper Dam is essentially brimming. That level is partly deliberate. The power scheme needs hydraulic head: the higher the water level, the more energy available from each release.
Why small dams still matter
The Steenbras pair is not where Cape Town keeps most of its water. Theewaterskloof holds roughly half the system on its own. Berg River, Voelvlei, and Wemmershoek carry most of the rest. Steenbras is 7.5% of total storage.
But size is not the only way a dam earns its place. The City has pointed to two things that make Steenbras useful: its height, which keeps gravity supply to large parts of the city cheap and reliable, and the flexibility it gives the network when other sections go offline for maintenance.
During the 2017-2018 drought, every megalitre mattered. Steenbras Lower dropped to critically low levels alongside the rest of the system. The 2022 centenary of the Lower Dam was marked with some ceremony, a plaque and a mayoral visit, partly because Cape Town does not have many centenary infrastructure moments left, and partly because the engineers who built it in three years with 1918 technology deserve the acknowledgment.
What to watch
At current draw rates, the combined Western Cape dam levels are tracking slightly below last year but well above danger. The winter rain season, which does most of the refilling work from May through July, is largely done for 2026. The next meaningful question is how much the system loses to evaporation and consumption across the dry months.
Steenbras Upper at 99.2% provides a useful buffer. Lower at 53.9% is mid-range normal for this time of year.
The live dam levels page updates every week from Department of Water and Sanitation reports. If the gap between Upper and Lower narrows sharply, meaning the Upper reservoir is being drawn down rather than held as a power-scheme reserve, that would be worth watching. For now, both dams are doing their jobs.