'Natural, human-induced factors behind Lake Bunyonyi’s strange appearance'

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The Ministry of Water and Environment has confirmed that a combination of natural and human-induced factors is responsible for the recent brownish cloud, foul odour, oily film and white cream seen on the surface of Lake Bunyonyi, one of Uganda’s most iconic and ecologically fragile water bodies.

Over the past three weeks, residents and visitors to the lake have raised concerns about the unusual appearance and smell of the lake, which have persisted longer than typical post-rainfall changes. 

Traditionally, rain-induced water discolouration in the lake clears up within days. However, the current situation has lingered, prompting urgent investigation by the ministry.

In a public statement issued on Monday, September 1, 2025, the ministry detailed the findings from a rapid environmental assessment involving water sampling, field inspections and interviews with local residents and stakeholders.

“Our field investigations show that the discolouration, foul odour and surface scum are the result of a combination of lake turnover triggered by heavy rainfall, runoff from steep agricultural slopes, degraded shorelines, and possible pollution from human settlements and commercial activities around the lake.”

According to the ministry, Lake Bunyonyi’s unique geographical location in a steep valley makes it highly vulnerable to runoff from surrounding hills. This runoff, often loaded with sediments and organic material, is likely contributing to the lake’s brown colouration and high turbidity levels.

Low oxygen levels

Laboratory analysis of water samples revealed alarmingly low levels of Dissolved Oxygen (DO), averaging just 1.60mg/L, which is considered hypoxic and harmful to aquatic life.

“These low oxygen levels point to a risk of eutrophication, where excessive nutrient enrichment causes rampant plant growth and oxygen depletion. This condition cannot support most fish species and threatens the lake’s biodiversity.” 

Additionally, the ministry confirmed that the National Water and Sewerage Corporation (NWSC) is facing difficulties in treating water from the lake to meet acceptable aesthetic standards, despite it being bacteriologically safe.

“The brown colour of the raw water, which has risen to 130 PtCo from typical levels of 30-45 PtCo during dry seasons, has affected public perception and forced some residents to seek alternative, less accessible water sources,” the ministry noted.

No evidence of volcanic activity

It also ruled out earlier speculation of volcanic activity beneath the lake.

“There is no evidence of volcanic activity. Such an event would have triggered tremors and caused flooding, which has not been reported,” the Ministry stated.

Human activities have also played a major role. About 46 hotels operate on the lake's shores, and while most have septic systems, there remains a risk of untreated wastewater entering the lake.

Furthermore, the Harutindo Landing Centre market, which lacks sufficient sanitation infrastructure, could be a key source of pollution.

Action plan

In response, the ministry has outlined a comprehensive action plan involving enforcement, community education, catchment restoration, and infrastructure development.

Short-term actions (within 1 year) include:

• Enforcing environmental regulations and inspecting establishments around the lake
• Mapping and protecting buffer zones to prevent encroachment
• Launching public awareness campaigns to link community activities to lake health
• Improving NWSC water treatment technology to manage high turbidity and colour
  
  Medium to long-term actions (1–5 years) will focus on:

• Demarcating and protecting catchment areas
• Promoting sustainable farming practices and erosion control measures
• Establishing proper waste management facilities at key public areas like Harutindo Market
• Providing alternative livelihoods to reduce pressure on lake ecosystems
  
  “We are committed to restoring the ecological balance of Lake Bunyonyi to safeguard its future as a vital resource for tourism, biodiversity, and community water supply.”

The ministry has promised a more detailed follow-up report by the end of September 2025, following ongoing investigations.

Lake Bunyonyi, known for its scenic beauty and unique biodiversity, remains a top tourism destination.

However, experts warn that without sustained intervention, its ecological and economic value could be severely undermined.