Four members of a group of ten fishermen have been killed after being attacked by Hippopotamuses by Lake Naivasha in Kenya on Friday 2 January 2025. The group, who have been described as local youths, approached the lake after dark as they lacked fishing permits, and are thought to have disturbed a group of Hippos with calves. Six of the party were able to escape by entering the water and swimming, or by climbing trees. One of the deceased is described as having initially escaped, but to have returned in an attempt to rescue a friend.
Lake Naivasha is noted for undergoing marked variations in its depth, and therefore extent. Water levels in the lake dropped continuously during the first half of the twentieth century, falling to 60 cm in 1945, then rose steadily for over two decades, reaching 6 m in 1968. The waters then fell until 1987, when the lake was only 2.25 m deep, but have been trending upwards since this time, causing the land to expand, swamping low lying villages and farmland, something which has accelerated in recent years as warming global temperatures have led to increased rainfall in East Africa.
One upshot of this that the lake naturally contains no commercially harvestable fish, probably as a result of drying up on occasions in the past. Non-native fish have been introduced to the lake in order to create a commercial fishery, but this has proven difficult to manage, with a dramatic fish-population crash fuelled by overfishing in 2001 leading to the introduction of strict fishing regulations on the lake.
This has created in a fish stock available to commercial fishing companies, and foreign tourists, but not to local villagers, resulting in frequent attempts to circumnavigate the regulations, for example by fishing at night. This has become more of a problem as the lake has expanded, swallowing up farmland and leaving the local population looking for other sources of sustenance. The expansion of the commercial flower growing industry, which earns the nation hard currency but also takes up farmland in the Rift Valley around lakes such as Naivasha and employs a relatively low number of people, has also tended to push people towards illicit economic activities such as night fishing, as well as fuelling conflict between Humans and aquatic wildlife such as Hippopotamuses and Crocodiles.
Flooding in a community beside Lake Naivasha in November 2025. Tony Karumba/AFP. While Hippos can appear benign to people unfamiliar to them, they are generally considered to be one of the most dangerous Animals in Africa, and probably the world. Hippopotamuses are the largest land Mammals after Elephants and Rhinoceroses, as well as being the closest terrestrial relatives of Whales. Adult Hippos typically weigh about 1.4 tonnes (males tend to be slightly larger than females, but this is marginal, and the sex of Hippos can be hard to differentiate). Hippos can open their mouths to almost 110°, and their jaws are highly muscled, allowing them to slap there mouths shut abruptly, driving canine and incisor teeth that can be 50 cm long into anything which offends them. This weapon is primarily used in intraspecific fights particularly between the males, which are highly territorial. However, they are also notoriously aggressive towards other species, particularly Humans, possibly as a result as having evolved alongside Pliocene and Pleistocene hunting Hominids. Hippopotamuses tend to stay in the water during the day, lowering the threat they present to Humans, but come out of the water to graze at night, when they are generally considered to be at their most dangerous.
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