An 1891 Anglo-Portuguese treaty fixed the southern borders of what had been renamed the British Central Africa Protectorate. Although the Ruo River had been the provisional boundary between Portuguese and British spheres of influence since 1879, as part of the 1891 treaty and under strong British pressure, an area west of the Shire and south of its confluence with the Ruo which had been controlled by an Afro-Portuguese family, was allocated to Britain and now forms the Nsanje District. The treaty also granted Britain a 99-year lease over Chinde, a port at one of the Zambezi delta mouths where sea-going ships could transfer goods and passengers to river boats. The northern border of the protectorate was agreed at the Songwe River as part of the Anglo-German Convention in 1890. Its western border with Northern Rhodesia was fixed in 1891 at the drainage divide between Lake Malawi and the Luangwa River by agreement with the British South Africa Company, which governed what is today Zambia under Royal Charter until 1924.