The science behind Kenya's transforming alkaline lakes

Flamingos at Lake Bogoria in Baringo County. [File, Standard]

A few weeks ago, pictures of Lake Bogoria covered in what seemed like a white sheet, almost like snow, resurfaced online, sparking widespread interest and curiosity across social media about what was truly happening in the iconic Rift Valley Lake.

What appeared to be a strange winter landscape was actually the aftermath of a massive algae bloom.

"This is something that normally happens in the lake a couple of times a year, depending on how the rain patterns are," explained Lake Bogoria Warden James Kimaru.

 According to Kimaru, these algae explosions are a regular occurrence influenced by changing weather, rain and temperature. These factors alter the lake’s water quality almost overnight.

“This phenomenon is often seen in one day before the lake turns back to its normal colour,” Kimaru explains.

He noted that when fresh rainwater fails to dilute the lake, the water chemistry changes, setting the stage for intense algal crashes.

Environmental scientists emphasise that the changing weather patterns are only part of the equation. They blame human activity upstream for accelerating the problem.

According to scientist Paul Gacheru, in closed ecosystems like Lake Bogoria, rivers feeding the lake pass through agricultural zones where synthetic fertilisers are heavily used.

“When rains wash nitrogen and phosphorus into these feeding rivers, the runoff mixes directly with the lake’s alkaline water, creating a perfect environment for mass growth of algae. When these massive blooms die off, millions of dead cells float to the surface to form a thick, white, blanket-like sheet across the water,” he explained.

“These issues stem from catchment management, where nutrients from farms and even sewage catalyse the growth of algae,” Gacheru added.

To understand why Rift Valley alkaline lakes undergo dramatic transformations, scientists say there are different types of algae. In highly alkaline lakes of the East African Rift Valley, three types of algae compete for dominance. One of them is Spirulina, a non-toxic, blue-green algae that thrives in alkaline soda lakes.

This alga forms the primary diet for millions of Lesser Flamingos and is responsible for the pigments that give them their iconic pink plumage.

When water levels drop during dry periods and salinity increases, a salt-tolerant algae takes over.

To protect themselves from intense sunlight and extreme salt concentrations, they produce deep red pigments, causing alkaline lakes to turn a vibrant watermelon-red or deep crimson.

 When water chemistry breaks down due to farm runoff or severe salinity shifts, healthy Spirulina populations crash, allowing dangerous algae to take over. These toxic algae directly target the liver.

This biological tug-of-war is not unique to Lake Bogoria. Similar bloom-and-crash cycles have been observed in alkaline water bodies such as Lake Magadi and Lake Natron in Tanzania.

At Lake Magadi, extreme evaporation during dry seasons creates high salt concentrations that trigger massive red algal blooms, which provide short-term feeding for flamingos.

In Lake Natron, the primary breeding ground for over 75 per cent of East Africa’s Lesser Flamingos, the stability of algal blooms dictates the survival of the entire species. When toxic algal blooms replace Spirulina at Lake Natron, adult flamingos ingest lethal doses of liver toxins.

When combined with starvation from a lack of edible algae, the results are devastating, historically causing mass bird die-offs. Under stress, flamingos are forced to abandon their nesting sites and fly hundreds of kilometres across the Rift Valley in search of cleaner waters, a demanding migration that disrupts breeding cycles for years.

Gacheru warns that algal bloom collapses do not only affect soda lakes.

They also affect freshwater lakes. When massive algal blooms are experienced in freshwater bodies, they consume large amounts of oxygen, stripping the water of life-sustaining oxygen.

“It is becoming a common occurrence in some areas to wake up to mass deaths of fish due to a lack of oxygen in the water as a result of changing water chemistry,” Gacheru said.

“During these severe die-offs, bacteria take over the decomposition process, releasing foul smells like rotten eggs. This destructive cycle plays out in freshwater rivers, lakes, seas, and oceans worldwide, where nutrient runoff creates massive marine "dead zones" that suffocate fish populations and bleach sensitive coral reef systems.