The Basin

The Orange-Senqu River Commission (ORASECOM) is a key partner in the collective management of the Orange-Senqu River Basin. It brings together the four riparian states – Botswana, Lesotho, Namibia and South Africa – to collaboratively manage the Basin’s shared water resources.

The Orange-Senqu River Basin – From source to sea

Covering nearly one million square kilometres, The Orange-Senqu River Basin spans four Southern African countries. Rising in the mountains of Lesotho, the river flows westward across diverse and often fragile ecosystems, from the Nama Karoo, Namaqua and Richtersveld in South Africa, to the Southern Kalahari in Botswana and the Namib Desert in Namibia.

The basin includes five wetlands of international importance recognised under the Ramsar Convention, reflecting its role as a biodiversity hotspot for birds and wildlife.

Known as Senqu in Lesotho and the Orange River downstream, the river is highly engineered, with dams and transfer schemes that support water supply, agriculture and hydropower across the region.

The Orange-Senqu River Basin is a critical lifeline for Southern Africa, directly supporting the livelihoods of 15 million people.

What is a river basin?

A river basin is an area of land where rainfall collects and drains into a shared river system. It includes rivers, wetlands and dams, as well as the surrounding landscapes where water is stored and flows both above and below ground. Basins are often defined by natural features like mountains or hills.

Because rivers do not follow political borders, many basins are shared by more than one country. These transboundary systems require cooperative and peaceful management between neighbouring states.

Managing the transboundary Orange-Senqu River Basin collectively

Protecting the source of the Orange-Senqu River in Lesotho is critical – not only for Lesotho’s own water, food and energy security, but also to meet the transboundary obligations shared between four countries. These include the 1986 treaty with South Africa that underpins the Lesotho Highlands Water Project.

Lesotho

The water tower of Southern Africa

The Mountain Kingdom of Lesotho is the source of the Orange-Senqu River. The river rises in the Maloti Mountains near Thabana Ntlenyana,Southern Africa’s highest peak, before flowing westward through the region.

The Maloti Mountains form part of the Maloti-Drakensberg Transfrontier Conservation Area and support a unique Afro-Montane biome. High rainfall and seasonal snow – up to 1 500 mm annually – make Lesotho a vital water source for the wider Basin.

As climate change increases the frequency of droughts and floods, ReNOKA, in partnership with ORASECOM, is supporting the restoration of degraded sub-catchments in Lesotho to strengthen climate resilience and protect vulnerable communities.

Lesotho’s catchment management areas

All the major rivers in Lesotho are tributaries of the Orange-Senqu River, including the Mohokare (Caledon), Malibamat’so and Senqunyane rivers. For strategic planning, these river systems are organised into six catchment management areas: Upper, Middle, and Lower Mohokare; Upper and Lower Senqu; and Makhaleng.

ReNOKA and government partners are developing Integrated Catchment Management Development Plans for each area, providing five to ten-year guidance on climate-resilient and sustainable land and water management.

These catchments are further divided into 74 sub-catchments, where ReNOKA supports community-driven action plans that address land degradation, improve livelihoods and build resilience.

Planning for the first two Integrated Catchment Management Development Plans , covering the Upper Mohokare and Makhaleng catchments, began in 2023. The process has progressed through technical baseline studies, stakeholder consultations, and institutional review.

In 2025, work began on four additional ICMDPs to extend integrated catchment planning to the remaining Catchment Management Areas: Lower Mohokare, Middle Mohokare, Upper Senqu, and Lower Senqu. These plans follow the same structured approach and are aligned with national policies and institutional frameworks.

Building on this foundation, ReNOKA has expanded beyond the initial pilot work in six sub-catchments. Drawing on lessons learned, integrated catchment management is now being scaled up in a further ten sub-catchments.

South Africa

South Africa contains 64% of the Orange-Senqu River Basin and is heavily dependent on water originating in Lesotho, particularly to support its industrial economy and the densely populated province of Gauteng.

The Vaal River, the largest tributary of the Orange River in South Africa, plays a central role in supplying water to the country’s economic heartland. Since 1923, the river has been extensively regulated through a system of dams designed to increase storage and manage growing demand.

Johannesburg is the single largest water user in the Basin. Founded following the discovery of gold in 1886, the city was not built on a natural river system and relies almost entirely on transferred water to meet the needs of its large and growing population. With the Lesotho Highlands Water Project, Lesotho has been increasing its water transfer to South Africa.

Botswana

Botswana is defined by striking water contrasts. In the north, the Okavango River forms the world’s largest inland delta, expanding dramatically during seasonal floods. In the south, much of the country is dominated by the Kalahari Desert and the Makgadikgadi Pans – remnants of an ancient inland sea that periodically come alive after rainfall.

Botswana forms part of three major transboundary river basins: the Okavango, the Limpopo and the Orange-Senqu. However, growing water demand driven by mining, energy and urban development places increasing pressure on limited water resources.

To address long-term water security, plans are underway for the Lesotho-Botswana Water Transfer Scheme. This proposed project would transfer water from Lesotho to Botswana and South Africa via the Makhaleng Dam, through a transfer system extending 700km.

Within the Orange-Senqu system, the Molopo River rises in Botswana and flows south-west to join the Orange River at Mahikeng.

Namibia

Namibia forms the lower reach of the Orange-Senqu River Basin, , where the river flows along the border with South Africa before entering the Atlantic Ocean at Oranjemund. The country accounts for approximately 7.9% of the Basin.

Upstream dams, including the Gariep and the Vanderkloof Dams, have significantly altered natural river flows over time. These changes have made coordinated management of the lower Orange River and its estuary increasingly important.

The Orange River Mouth was designated a Ramsar wetland of International importance in 1995 in recognition of its role in supporting coastal fisheries, providing a habitat for breeding birds, and limiting salt water intrusion.

Regional cooperation between ORASECOM and Namibia’s Benguela Current Commission (BCC) in Namibia supports integrated catchment management of the river and estuary. Through regulated releases, the estuary is flooded annually to sustain its ecological function. A further dam proposed at Vioolsdrift in South Africa is intended to improve flood regulation for the lower Orange River.

Along the Northern Cape and Namibian border, the Orange River sustains the arid Namaqualand and Richtersveld biomes, which host unique plant and animal species adapted to extreme conditions.

Namibia’s Fish River, home to Africa’s largest canyon, is an intermittent tributary of the Orange River. While usually dry, its scale reflects a wetter geological past and highlights the region’s long-term environmental change.

Catchment restoration needs a long-term and multi-sectoral approach. Read about how ReNOKA does things differently.

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