Salvinia Weed Threatens Lake Victoria's Ecosystem.

Lake Victoria Faces Growing Threat from Invasive Salvinia Weed

Mwanza March 4, 2025

Lake Victoria is grappling with an escalating threat from an invasive aquatic weed, Salvinia, which has significantly impacted the transport sector. This new weed attaches itself to the bottoms of marine vessels, particularly propellers, posing a severe challenge to navigation.

The National Environment Management Council (NEMC) Lake Zone Manager, Jarome Kayombo, revealed that the weed was first identified in August 2024. Investigations have since linked its emergence to human activities, particularly agricultural practices along the lake's shoreline.

Salvinia thrives on the abundant nutrients present in Lake Victoria, multiplying at an alarming rate, with research indicating it can grow two to three times over within just eight days. "This rapid growth indicates that the lake's ecosystem is becoming increasingly polluted," Kayombo said.

A task force set up to investigate the weed’s spread found that agricultural runoff, especially during the rainy seasons, is a key contributor. This runoff carries harmful plants into the lake, enabling Salvinia to take root. Kayombo also noted that wind patterns exacerbate the weed's spread, further complicating control efforts. In a span of just four days, the task force collected 36 tonnes of the weed, but it had already regenerated by the following day, showing how quickly it multiplies.

Violations of environmental laws, such as illegal farming within 60 meters of the lake, have worsened the situation. The destruction of natural vegetation allows harmful substances to enter the water unfiltered, contributing to the proliferation of the weed.

The spread of Salvinia is having severe consequences for aquatic life. By forming dense mats on the lake’s surface, it blocks oxygen from reaching deeper waters, disrupting marine life and breeding cycles. Fish farming has been particularly affected, as the weed forms dense mats around fish cages, making it impossible for farmers to feed their fish.

So far, the infestation of Salvinia remains confined to Tanzania’s portion of Lake Victoria, with no reports of the weed spreading to Uganda or Kenya. Kayombo mentioned that Uganda had previously encountered Salvinia in a smaller water body before it reached Lake Victoria, but they had successfully managed to control it.

Kayombo called for collective action to protect Lake Victoria, stressing the importance of proper waste management practices. "Communities and families must play their part in safeguarding the lake," he said. "We also urge investors to adhere strictly to environmental regulations, as some are exceeding their permits and contributing to further contamination."

One of the most concerning examples highlighted by Kayombo involved a fish farmer who set up 400 cages in an area designated for just 20, exacerbating pollution and spreading the infestation. Researchers are continuing their efforts to find effective solutions to combat the Salvinia invasion.

Irene John, NEMC’s Communications Manager, underscored the importance of preserving Tanzania’s environment. "Tanzania is our only home. If we fail to protect it, we have nowhere else to go," she said.