The Serengeti ecosystem hosts the annual wildlife migration of up to 2 million animals (mainly wildebeests, zebras and other species of the plains). It is a World Heritage site, important to the Tanzania tourism industry, and an ecosystem living laboratory. It comprises the Serengeti National Park, the Masai Mara National Reserve in Kenya, and several Conservation, Game, and Wildlife Management areas. The Serengeti has one perennial river, the Mara, which is the only source of water for migrating wildlife in a drought year. The Mara River is formed by the confluence of the Amala and Nyangores Rivers, which drain the Mau forest in the Kenyan highlands; it is a transboundary river shared between Kenya upstream and Tanzania downstream (Fig. 1).

Fig. 1 The Serengeti ecosystem, comprising the Serengeti National Park in Tanzania, the Masai Mara National Reserve in Kenya, and several Conservation, Game, and Wildlife Management areas, with the locations of eight proposed dams (seven in Kenya and one in Tanzania), the catchment boundary of the Mara River formed by the confluence of the Amala and Nyangores Rivers that drain the Mau forest of the Transmara Forest Reserve and other areas, and the typical wildebeest migration routes and their timing during non-drought years. The Amala transfer would divert Amala River water impounded behind the proposed Amala High dam through a tunnel to the Ewaso Ngiro River. Protected area boundaries are from the World Database on Protected Areas (http://protecedplanet.net) of June 2017.

Under the framework of the Nile Equatorial Lakes Subsidiary Action Programme, and with the technical support of UNESCO-IHE, the Kenya Water Resource Management Authority has developed a water allocation plan for the Kenyan side of the basin (http://nelsap.nilebasin.org/index.php/en/). This includes plans for constructing (1) the 10 m high Norera dam on the Mara River, mainly for irrigation c. 30 km upstream of the Serengeti, (2) the 65 m Amala High dam in the Mau forest, with provision for water transfer through a tunnel from the Amala River to the Ewaso Ngiro River for hydroelectricity generation by three dams (Oletukat Olenkuluo, Leshoto and Oldorko; 140, 57 and 30 m high, respectively) and discharge of that water to Lake Natron in Tanzania, and (3) one or two dams (Mungango and Silibwet, 30 and 70 m high, respectively) on the Nyangores River, mainly for irrigation (Fig. 1). None of these dams have yet been constructed, but the feasibility studies, except that for the Amala High dam, were completed by 2016. Tanzania is proposing the Borenga dam. The feasibility study is completed but the dam has not yet been built; it is located downstream from the Serengeti and thus creates no water threat to this ecosystem.

The Kenya dams pose a direct threat to the Serengeti: (1) The Norera dam would release a minimum environmental flow (MEF) of 100 litres per second, only 1/3 of the Mara River MEF recommended by the Lake Victoria Basin Commission of the East African Community. (2) That same water would then flow through 30 km of intensive irrigation farming, and thus the Mara River would be dry on entering the Serengeti. (3) The Norera dam would receive 39% of its water from the Nyangores River; the two irrigation dams on the Nyangores (Mungango and Silibwet) would decrease the low flow by 100 litres per second, but this impact was not included in the Norera dam proposal and doubles the chances that this dam will not release the MEF. (4) The Norera proposal is based on a mean annual flow calculated over 22 years of data, but in a dry year the annual flow is only 51% of the mean flow and thus in such a year the operator has only half of the water expected. Being short of water, the Kenyan operator has either to release the MEF for the Serengeti and kill the irrigation fields and hurt the local community, or retain the water for irrigation and kill the Serengeti. This becomes a local political decision, with Tanzania having no say. (5) The World Bank Safeguard Policies have been breached twice by the proposal, which states incorrectly that the Mara River is not an International Waterway and that the development does not affect the forests. (6) The total annual storage and use would be 115–185% of the annual flow in a drought year, and hence the dams require more water for irrigation than is available, leaving nothing for MEFs. (7) The Amala High dam would destroy the Mau forest, and this would further decrease the Mara River dry season flows (Mango et al., 2011, Hydrology and Earth System Sciences, 15, 2245–2258). (8) During the dry season in a drought year there would be zero MEF for the Masarua swamp. (9) Seventy-five percent of the world's lesser flamingos are born around Lake Natron. The diversion of Mara River water to the lake will flood their nesting sites.

If the wildebeests cannot use the Mara River (their only water resource in the dry season in a drought year), modelling studies suggest that 80% may die (Gereta et al., 2009, Ecohydrology & Hydrobiology, 9, 115–124), leaving behind a much-impoverished ecosystem. To save the Serengeti ecosystem an international effort is needed to enable Tanzania to be involved as an equal partner with Kenya in the decision-making about managing the Mara and Ewaso Ngiro Rivers and, if that is not possible, to prevent the financing of these dams.