Invasive alien species (IAS) are non-native organisms that spread and harm ecosystems. Kenya’s tropical climate and many disturbed habitats make it vulnerable to invasions. The water hyacinth (Eichhornia crassipes) is a classic example: introduced to Lake Victoria around 1988, it exploded into vast mats. By 2020 it covered over 1,700 hectares of Lake Victorianews.mongabay.com, clogging fishing lanes and hydroelectric intakes. Hyacinth depletes oxygen, killing native fish and altering water chemistry. Local groups now harvest hyacinth for compost and biofuel, but blooms return annually with rains.

• Prosopis (Mathenge): This thorny tree from Latin America was planted decades ago to control desertification in northern and eastern Kenya. It backfired – Prosopis now infests up to a million hectares in ASAL (Arid and Semi-Arid Lands), shading out grasses and acacias. Dense Prosopis thickets make land unusable for wildlife or livestock. In late 2024 Kenya launched a campaign to clear Prosopis from Lake Bogoria (Baringo County) after it was linked to lesser flamingos’ deathsblog.invasive-species.org. That removal suggests the direct threat: an invasive shrub caused a crash in one of the world’s great flamingo breeding sites.
• Plants (Weeds): Other invasive weeds include Lantana camara (an ornamental shrub) and Parthenium hysterophorus (a toxic annual). Lantana now infests forest edges and farmlands in highland areas, crowding out native trees and even deterring coffee harvesters (its thorns scratch livestock). Parthenium is spreading rapidly in central Kenya grazing lands; the government now lists it as an obnoxious weed because it poisons livestock and disrupts soil microfauna. No comprehensive data exists, but entomologists note that invasive plants often co-occur with declines of native grassland plants.
• Aquatic Invasives: Beyond hyacinth, lakes have other invaders. Blue-green algae (cyanobacteria) sometimes explode in polluted, warm waters, creating toxins harmful to fish and birds (as in parts of Lake Nakuru). In Lake Naivasha, the ornamental plant Potamogeton and invasive tilapia strains have altered fish communities. Marine invasives are less common, but even small introductions (e.g. alien oysters on coral reefs, or the seaweed Caulerpa) could pose future risks.
• Animals and Pathogens: While large vertebrates are few, some invasives appear: the small Indian mongoose was introduced in the mid-1900s to control snakes, and now preys on ground-nesting birds. Weed biocontrol insects (like moths on Opuntia) have their own risks. More critically, climate change and trade increase disease invasion; recent African swine fever or avian flu outbreaks demonstrate how a pathogen can wipe out native species or farm animals.

In summary, invasive species silently reshape many Kenyan ecosystems. Shallow lakes and wetlands often see the worst effects (from hyacinth choking fish to Prosopis drying springs). Even remote parks can be invaded: East Africa’s Rift lakes, forest reserves and even urban waterways must now contend with alien flora. Tackling invasives requires sustained control – physical removal, herbicides or bio-control – and robust monitoring. Kenyan authorities have begun mapping problem species (e.g. national surveys for Prosopis and parthenium), but experts caution that prevention (strict controls on plant trade) is more efficient than cure. In all, invasive species compound other drivers: a forest cut by logging may become overrun by exotic weeds, or a lake stressed by pollution may be tipped to an algal-dominated state. Kenya’s biodiversity management plans now list several key invasives (water hyacinth, Prosopis, Lantana) as top threats, alongside habitat loss and climate change.