Malawi–Tanzania border

A British–German line between two lakes

The border began as a line between British and German spheres of influence. The Anglo-German agreement of 1 July 1890, often called the Heligoland–Zanzibar Treaty, roughly set out the two powers' territories between Lake Tanganyika and Lake Nyasa, and in Lake Nyasa itself.^[1][2]

The land section was fixed in detail later, after a joint boundary commission in 1898 and an agreement signed in Berlin on 23 February 1901.^[1] It follows the Songwe River up from the lake, then the small Katende stream to longitude 33°E, and then a straight line southwest to the top of Nakungulu hill, on the watershed of the Congo basin. A watershed is the high ground that divides two river systems.^[1] The 1901 agreement also made clear that where a river forms the border, the line runs down the middle of its bed.^[1]

“It begins at the mouth of the Songwe River at Lake Nyasa and follows this river upwards to its junction with the Katendo (Katende) Stream in the Shitete district…”^[1]

The shore, not the middle

In the lake, the 1890 agreement did not split the water. Its line starts at the Mozambique tripoint on the eastern shore and follows the eastern, northern and western shores of the lake to the Songwe.^[1] That left the whole northern part of the lake on the British side, in what became Nyasaland and then Malawi.^[2] In 1964 the US Geographer noted that a number of texts and maps wrongly showed a median line in the lake instead of the shore named in the treaty.^[1]

The southern end moved slightly in 1907, when a German–Portuguese commission shifted the tripoint about half a kilometre south, to the mouth of the Txuinde stream.^[1] The lake's level rises and falls a great deal from season to season and year to year, which makes the exact shoreline hard to pin down. In 1964 the US Geographer suggested the shore line might one day need more detailed definition for that reason.^[1]

Britain ran both sides from the First World War, when German East Africa became the British-run mandate of Tanganyika, until independence. Tanganyika and Malawi both accepted the existing boundary when they became independent.^[1]

The lake dispute

Malawi's position is that the border follows the shoreline, as the 1890 treaty says. Tanzania's position is that the border should run down the middle of the lake, citing the international practice of dividing lakes at the median line, the line halfway between the shores.^[2][3] Tanzania also points to the lake's Malawi–Mozambique section, which has followed a median line since 1954.^[3]

Officials of the two states argued briefly in 1967–68, with no clear outcome.^[2] Tanzania did not pursue the claim as government policy, and in line with the 1964 Cairo Declaration it recognised Africa's borders as they stood at independence. Its first president, Julius Nyerere, conceded the boundary.^[2]

The dispute returned after Malawi's President Bingu wa Mutharika, in October 2011, awarded a UK company a contract to explore for oil and gas in the eastern part of the lake, including the area Tanzania claims.^[2] The company was Surestream.^[3] The two countries turned to mediation through the Southern African Development Community (SADC), led by former Mozambican president Joaquim Chissano, alongside Thabo Mbeki of South Africa and Festus Mogae of Botswana.^[2] In April 2013 Malawi briefly withdrew, alleging bias by a SADC official, and returned in May.^[3]

The mediators held their last negotiations in July 2017, and a meeting planned for 2018 was cancelled at the last minute. Writing in 2023, analysts at RUSI said the dispute had entered a state of limbo.^[2] The map above follows Natural Earth, which draws the line along the eastern shore. It does not show Tanzania's claimed median line.

Along the Songwe

The land border divides the lands of the Lambya and Nyakyusa peoples. In 1964 most people there farmed, and fishing on the lake was important.^[1] Only trails and tracks crossed the border then, and lake steamers from Monkey Bay in Malawi had served Tanganyikan ports until a rise in the lake level disrupted them.^[1]