Prioritizing conservation in sub-Saharan African lakes based on freshwater biodiversity and remote-sensing algal bloom metrics

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Figure 1. Hydrologically relevant watersheds in the study area: (a) Ghana, (b) Ethiopia, and (c) Zambia. Watershed colors are based on level 3 and level 4 HydroBASINS.
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Figure 5. Lakes of conservation priority in (a) Ghana, (b) Ethiopia, and (c) Zambia, prioritized according to freshwater species richness and normalized difference chlorophyll index (NDCI) values. Many of the lakes identified in Ethiopia and Zambia are in watersheds that cross political boundaries.
Background

Freshwater lakes support a large share of global biodiversity and provide essential services such as food security, drinking water, and livelihoods. Across sub-Saharan Africa, these ecosystems are under growing pressure from expanding agriculture, nutrient runoff, and climate-driven warming. One major consequence is the increasing risk of harmful algal blooms, which degrade water quality, reduce oxygen levels, and release toxins that threaten both wildlife and human health. Despite these risks, many African freshwater systems lack consistent monitoring due to limited resources and logistical challenges. We identified a critical need for spatially explicit information to determine where biologically rich lakes are most vulnerable to emerging water quality threats.

Approach

We developed a spatial framework that combines satellite observations with freshwater biodiversity data to identify conservation priorities at a regional scale. Using cloud-based computing, we analyzed tens of thousands of high-resolution satellite images collected over multiple years to estimate algal bloom risk across more than 1,800 lakes in Ghana, Ethiopia, and Zambia. These satellite signals provide a reliable indicator of algal biomass and water quality trends. We then integrated this information with watershed-based species richness data for freshwater fish, mammals, birds, and other freshwater-dependent vertebrates. Lakes were classified as high priority when elevated algal risk coincided with above-average biodiversity.

Key Findings

We identified clear and actionable conservation patterns across the three countries:

  • Priority Lake Identification: We identified 169 lakes or lake regions where high freshwater biodiversity overlaps with elevated algal bloom risk, marking them as urgent conservation priorities.
  • Strong Regional Differences: Zambia contained the largest number of priority sites, reflecting widespread eutrophication risk alongside high species richness. Ethiopia showed moderate but widespread risk, while Ghana had fewer priority lakes, largely concentrated near densely populated areas.
  • ​Transboundary Vulnerability: Many high-priority lakes occur within watersheds that cross national borders, indicating that freshwater threats extend beyond political boundaries and require coordinated management.
Overall, the results demonstrate that satellite-based monitoring can successfully reveal “biological conflict zones” in regions that are otherwise difficult to study.

Impact

This work demonstrates how remote sensing can directly support freshwater conservation planning where on-the-ground monitoring is limited or unavailable. By identifying specific lakes where ecological value and environmental risk intersect, we provide a practical tool for guiding conservation investments, informing policy decisions, and encouraging cross-border cooperation. The framework is cost-effective, scalable, and adaptable, offering a pathway to proactively protect vulnerable freshwater ecosystems in Africa and beyond as climate and land-use pressures intensify.

Resources

​Published paper : Danaher* C, Newbold T, Cardille J, Chapman ASA. Prioritizing conservation in sub-Saharan African lakes based on freshwater biodiversity and remote-sensing algal bloom metrics. Conserv Biol. 2022. ​DOI : https://doi.org/10.1111/cobi.13914