By Faith Barbara N Ruhinda at 1142 EAT on Monday 25 August 2025

A new scientific review has raised serious concerns about the environmental impact of cage fish farming in Lake Victoria, warning that the practice is depleting native fish stocks and could trigger a long-term ecological crisis.

The review, titled “Environmental Impacts of Cage Fish Farming: A Review,” was co-authored by Barirega Akankwasah, Executive Director of the National Environment Management Authority (NEMA), alongside six other experts.

• Eutrophication: Waste from uneaten fish feed and faecal matter—rich in nitrogen and phosphorus—leads to nutrient overload in the water. This promotes excessive algal blooms, which in turn deplete dissolved oxygen levels and create toxic conditions that threaten aquatic life.
• Disease Transmission: The open nature of cage fish farming facilitates the spread of diseases and pathogens between farmed fish and wild fish populations, posing a significant risk to the health and stability of native species.
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  Alterations in Aquatic Biota: The accumulation of waste products can disrupt the natural balance of aquatic ecosystems, leading to shifts in species composition and the decline of sensitive or native species.
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  Degraded Water Quality: The buildup of ammonia and other harmful byproducts from fish waste poses a serious threat to water quality, potentially impacting both aquatic life and surrounding communities that rely on the Lake.

A separate study conducted by Kenyan researchers recorded ammonia concentrations around fish cages ranging from 0.14 to 0.2 mg/L—levels that, while seemingly low, can still be toxic to fish and other aquatic organisms.

These findings reinforce concerns raised in a separate study published less than two months ago, which specifically warned of the ecological and genetic risks associated with Nile Tilapia cage aquaculture in Lake Victoria.

The study warned that escaped farmed fish could interbreed with wild populations, leading to a loss of genetic diversity and potential disruption of Lake Victoria’s delicate ecosystem. While acknowledging the economic appeal of cage farming—where a single 8–12 m³ cage can yield up to one ton of fish in just eight months—the researchers cautioned that such benefits may come at the expense of the lake’s long-term ecological health.

They cited the mass fish die-offs reported in January 2021 at several landing sites in Wakiso District as a possible consequence of environmental degradation linked to intensive aquaculture practices.

To avert further ecological harm, the NEMA-led review recommends that any future expansion of cage fish farming must be guided by stringent environmental safeguards, including advanced waste management systems and continuous ecological monitoring.

A separate study by researchers from the Kenya Marine and Fisheries Research Institute stressed the urgent need for a clear policy framework to guide lake zonation. Such a framework, they argue, is essential to ensure that all stakeholders—including fish farmers, local communities, and conservation groups—can utilize Lake Victoria’s resources sustainably and without causing environmental harm.

Without proper regulations in place, the report warns, the continued expansion of cage fish farming could lead to an environmental disaster.

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