World Lake Day

by Catherine Sayer, Eresha Fernando, Karen Murchie & Michael Edmondstone

‘Lakes’, in the words of the United Nations, ‘are one of the most vital natural resources on our planet. They serve as a crucial source of fresh water, supporting drinking water supplies, agriculture, and industry. [They] play a key role in maintaining biodiversity, offering a habitat for countless species of fish, plants, and wildlife, and contribute to climate regulation by keeping the planet cool, absorbing the floodwater and storing carbon¹.

But, like other freshwater systems around the world, lakes are affected – sometimes dramatically – by overuse, pollution, abstraction, invasive species, and climate change. Around half (48%) of extinct freshwater animals are lake-dwelling species, which is significant given that less than one fifth (18%) of threatened freshwater animals live in lakes²; in other words, a disproportionate amount of these species go extinct. 

Lakes are already facing serious decline. Inland wetland loss in terms of area lost since 1970 is greatest for lakes, according to the 2025 Global Wetland Outlook, at 31%. In comparison, inland marshes and swamps account for 27%, peatlands 13%, and rivers and streams 6%³. If current trends continue, by 2050, pollution will more than double, methane emissions will surge, species will be lost, and we will witness even greater catastrophic environmental damage and economic loss.

To help raise awareness, celebrate, and encourage action to preserve, conserve, restore, and sustainably manage these intricate ecosystems, the United Nations established the first World Lake Day on 27 August this year, serving as a rallying cry to governments, NGOs, researchers, educators, and local communities to come together through education, restoration efforts, cleanup campaigns, policy advocacy, and community-led conservation actions to ensure lakes around the world are given the best possible chances of thriving long into the future.

In this joint authorship piece, written by Eresha Fernando, IUCN Programme Officer for Freshwater, Catherine Sayer, Freshwater Biodiversity Lead at IUCN, Karen Murchie, Director of Freshwater Research at Chicago’s Shedd Aquarium, and Michael Edmondstone, Communications and Engagement Lead at SHOAL, we discuss conservation actions currently taking place in some of the world’s major lakes.

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Michael Edmondstone, SHOAL:

Protecting Endemic Fishes in Sulawesi’s Ancient Lakes: Lake Poso and Lake Lontoa

The Poso and Malili lake systems of Sulawesi are global centres of freshwater endemism, yet many of their species remain poorly known and increasingly threatened. Two recent projects supported by SHOAL partners – Progres in Lake Poso and Hasanuddin University in Lake Lontoa – illustrate both the urgency and the scientific dedication required to conserve these unique faunas.

Endemic ricefishes of Lake Poso

Lake Poso is home to six endemic ricefishes, including the Critically Endangered Adrianichthys kruyti and A. roseni, both of which have not been observed alive for decades. Progres has been leading efforts to verify their continued existence and strengthen local stewardship of the lake’s biodiversity. Over the course of 2024, Progres teams conducted regular monitoring surveys, typically twice a month at dawn and dusk, in collaboration with local ‘Rono’ fishers whose traditional ecological knowledge is crucial for guiding searches.

Although these rare Adrianichthys species remain elusive, surveys have documented other endemic ricefishes such as Oryzias nigrimas, O. nebulosus, O. orthognathus, and O. soerotoi. The findings underscore both the persistence of Poso’s endemic fauna and the gaps in knowledge about species once thought to be abundant. Progres has also invested heavily in community engagement, running education programmes with schools, training young people in survey techniques, and building conservation awareness among local fishing groups. These actions aim to ensure that any rediscovery of lost species is paired with long-term protection of their habitats.

The search for Paratherina labiosa in Lake Lontoa.

Lake Lontoa, part of the Malili Lakes system, is the only known habitat of Paratherina labiosa, a sailfin silverside considered Critically Endangered. Recent surveys by Hasanuddin University, in collaboration with local partners, sought to confirm its presence. Two intensive expeditions in July and October 2024 used gillnetting, baited traps, snorkeling, and even underwater drones, but failed to locate the species. While Oryzias marmoratus, several Telmatherina, and endemic gobies were observed, P. labiosa remained undetected.

The surveys also documented alarming environmental pressures. Deforestation around the lake, often for pepper plantations, has led to high sedimentation and nutrient runoff, with ammonia levels recorded up to 0.43 mg/L and iron concentrations above 1.0 mg/L, well beyond safe thresholds for aquatic biota. Algal blooms and reduced water clarity were noted, alongside invasive species such as Tilapia (Oreochromis mossambicus), Snakehead (Channa striata), and Climbing Perch (Anabas testudineus), all of which pose risks to native fish through predation or competition.

Despite the absence of P. labiosa records, the project has strengthened the baseline understanding of Lake Lontoa’s fauna and threats. Plans for further surveys – including environmental DNA analysis – offer hope of clarifying whether this enigmatic fish still survives.

Together, these initiatives in Lake Poso and Lake Lontoa highlight the dedication of local researchers and communities to safeguarding Sulawesi’s irreplaceable freshwater heritage.

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Karen Murchie, Shedd Aquarium

Love for the Laurentian Great Lakes

The catchy acronym for the Laurentian Great Lakes (LGLs) in North America is “HOMES” (representing Lakes Huron, Ontario, Michigan, Erie and Superior) that make up this incredible freshwater system holding 21% of the world’s surface freshwater. While it is a fitting way to remember the lake names, it is also a beautiful way to remember that these lakes are habitat for amazing aquatic species as well as the people choosing to live along their shorelines. From 139 native fish species, 47 native freshwater mussel species and even wild rice (manoomin), to the over 38 million residents within the watershed, there are many reasons to highlight the LGLs on the first World Lake Day.  

Beyond the threats identified earlier in this blog, urbanisation and a lack of connectedness to nature can exacerbate the threats to our lakes. As such, public aquariums play an outsized role in showcasing lakes by providing opportunities for guests to look freshwater species in the eye with engaging exhibits and interpretive graphics. Shedd Aquarium, in Chicago, is located on the south shore of Lake Michigan in the United States and believes sparking curiosity, compassion and conservation for the LGLs is a priority. Connections formed at Shedd are important because turbid, cold water often limits interactions among people, the lakes, and animals that call them home. However, at Shedd, guests can reach down and touch a massive Lake Sturgeon, count the stripes on a Yellow Perch, and learn how white suckers feed and migrate up dozens of Great Lakes tributaries, and act on behalf of the LGLs.  

Beyond education, aquarium team members take people, some of whom have never seen Lake Michigan, to walk along its edge and remove plastic and other debris before it enters the water where it can break down and harm wildlife. Last year, we removed over 6000 lbs (>2700 kg) of trash from Chicago area sites! Action Days activities lead to advocacy, where those who see plastic pollution as harmful to the environment can look for opportunities to enact meaningful legislation, such as limiting single use plastics.

Knowing how dire freshwater biodiversity loss is across the globe requires an increase in champions for healthy freshwater ecosystems. This has prompted ocean advocates including Dr. Sylvia Earle and her organisation, Mission Blue, to recognise the LGLs as the first-ever freshwater “Hope Spot” in 2023. This much needed recognition we hope will continue as the UN recognises World Lake Day each year and the invaluable ecosystem services these wonders provide. Greater appreciation and protections are exactly what our lakes around the world need to help restore habitats, reverse climate change and keep our freshwater biodiversity and our communities healthy and safe. 

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Eresha Fernando, IUCN

Incorporating Indigenous and Local Knowledge into IUCN Red List assessments of Lake Tanganyika freshwater fishes

The IUCN Red List of Threatened Species^TM4  is the world’s most comprehensive information source on the extinction risk of species. Typically, the Red List is based on scientific information, but there is now increasing awareness of the need to include knowledge from Indigenous People and Local Communities, with the aim of strengthening the overall evidence base used in IUCN Red List assessments.

Drawing on recent reports on the application of Indigenous and Local Knowledge (ILK) in IUCN Red List assessments⁵, and IUCN Guidelines for gathering of fishers’ knowledge for policy development and applied use⁶, IUCN recently applied this guidance into assessment work of freshwater fishes native to Lake Tanganyika. Lake Tanganyika, one of Africa’s Great Lakes, is a global hotspot for aquatic biodiversity, representing the largest freshwater reservoir in Africa supporting over 12 million inhabitants from the surrounding four riparian countries: Burundi, Democratic Republic of Congo, Tanzania, and Zambia)⁷.

Through the integration of ILK holders, including fishing community representatives, with intentional inclusion of women and young people to ensure diverse perspectives, IUCN were able to develop a dialogue between fishers and the local community, local authorities, and scientists. This dialogue has subsequently enabled ILK to be successfully incorporated into multiple IUCN Red List assessments of Lake Tanganyika freshwater fishes, and in some cases has led to the recognition of a higher extinction risk of certain species. 

This process has therefore not only proved the strengths of using both traditional and scientific knowledge systems, but has led to more comprehensive extinction risk evaluations of Lake Tanganyika freshwater fishes, and will ultimately support inclusive and locally-grounded conservation in lake systems.

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Native species aquaculture for conservation, economic growth and human nutrition in Lake Victoria

Lake Victoria, shared by Kenya, Uganda and Tanzania, is one of the sources of the famed Nile River. It is the world’s second largest lake by surface area (Lake Superior on the USA/Canada border is first) and the largest tropical lake. 

Historically, Lake Victoria was one of the world’s most biodiverse freshwater ecosystems, with the diversity anchored by its community of more than 500 endemic cichlid species that evolved there. These Lake Victoria cichlids – Haplochromides – come in an incredible assortment of sizes, display extensive differences in their diets and behaviours, and tend to be dazzlingly coloured, making them darlings of aquarists. Sadly, due to the combined forces of the all-too-common factors of habitat loss, over-fishing, pollution, and the deleterious impacts of exotic species (particularly the intentional introduction of the predatory Nile Perch in the 1950s; Lates niloticus), haplochromide populations throughout the lake are greatly reduced.

An additional threat to the native fishes of Lake Victoria, as is also happening in many other tropical lakes, is the recent and rapid expansion of cage-based aquaculture. In cage culture, “fingerlings”, (i.e. juveniles a few weeks old) produced in a hatchery are placed into floating nets, fed a commercially purchased fish food, and allowed to grow to marketable size and then harvested. Cage culture almost exclusively uses the non-native Nile Tilapia, a highly domesticated genetic hybrid developed for fast growth. While cage culture has been successful at producing a reliable and healthy human food supply and has provided new economic opportunity to a historically under-developed human community, it has also brought notable challenges. Unfortunately, in many instances, aquaculture cages are often located in the heart of the best habitat for the native fishes for the obvious reason that these locations have the best water quality for fish growth. For the native fishes, escape of the domestic Nile Tilapia leads to the native fishes being out-competed for food and displaced from their habitats by the more aggressive and faster growing exotics. Further, due to the high density of fish in the aquaculture cages, there can be extensive water quality degradation in proximity of the cages stemming from an over-abundance of nutrients from decomposition of undigested fish food and fish metabolic waste. 

Against this backdrop of general threat is the plight of two of the native haplochromide species, the Singida Tilapia (aka ‘ngege’; Oreochromis esculentus) and the Victoria Tilapia (‘Mbiru’; O. variabilis). Historically, these two species were dominant parts of the fish harvest from the lake and common parts of human diets. Due to the above noted factors, these fish are now Critically Endangered. 

Working in partnership with relevant government agencies and multiple private sector concerns, ranging from commercial scale aquaculture enterprises to start-up women’s collective cage culture organisations and regional farmers working to formulate locally produced fish feeds, our research group is trying to turn cage-culture into a potent tool for native species recovery. Our approach involves collecting specimens of these two species from the few remaining healthy populations found in the small satellite lakes near Lake Victoria and establishing a captive breeding programme. Twin goals of the breeding programme are i) to protect the genetic integrity of the different lineages and release progeny back to the wild once the limiting factors that caused the local extirpations have been rectified, and ii) use selective breeding techniques to produce strains of these two species suitable for cage-culture grow-out operations and thereby replace the non-native Nile Tilapia with these native species. Our research shows a few additional benefits. Firstly, in market evaluation, based on factors like cultural awareness and taste, we have found a strong human preference for the native fish over the exotic Tilapia. Hence, the potential exists to establish a ‘premium’ product that might yield higher profit margins, particularly from regional export markets that send fishes to the larger cities of the region. Secondly, the native fish appear to offer a distinctly different fatty-acid profile than the non-natives. These fatty-acids are essential parts of a healthy human diet, so it appears that moving the marketplace towards the native fishes may well yield human health benefits to complement the biodiversity conservation benefits.          

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Together, these efforts showcase the power of combining scientific assessment, policy designation, community capacity building, Indigenous and Local Knowledge, invasive species management, and long-term planning to ensure our world’s lakes thrive in the future.

As we observe the inaugural UN World Lakes Day, these examples from lakes Poso, Lontoa, Tanganyika, Victoria, and the Laurentian Great Lakes, stand as powerful emblems of both the fragility of freshwater ecosystems and humanity’s capacity to act. The dramatic changes to the balance of the lakes over the past few decades remind us why freshwater conservation must be urgent, local, collaborative – and full of hope.    

1. https://www.un.org/en/observances/world-lake-day
2. https://www.nature.com/articles/s41586-024-08375-z
3. https://www.global-wetland-outlook.ramsar.org/
4.  IUCN. 2025. The IUCN Red List of Threatened Species. Version 2025-1. https://www.iucnredlist.org. Accessed July 2025.
5.  IUCN. 2022. Application of Indigenous & Local Knowledge (ILK) in IUCN Red List assessments: White paper. Version 1. Adopted by the IUCN SSC Red List Committee and IUCN CEESP-SSC Sustainable Use & Livelihoods Specialist Group Steering Committee. https://www.iucnredlist.org/resources/ilk.
6.  Cowie, W., Al Dhaheri, S., Al Hashmi, A., Solis–Rivera, V., Baigun, C., Chang, K., Cooney, R., Kamaka‘ala, S., Lindeman, K., Louwa, C., Roe, D., Walker–Painemilla, K., Al Baharna, R., Al Ameri, M., Al Hameli, S., Al Jaberi, K., Alzahlawi, N, Binkulaib, R., Al Kharusi, Y. 2020. IUCN Guidelines for gathering of fishers’ knowledge for policy development and applied use. IUCN, Gland, Switzerland; and Environment Agency – Abu Dhabi, United Arab Emirates. https://iucn.org/resources/publication/iucn-guidelines-gathering-fishers-knowledge-policy-development-and-applied.
7.  Phiri, H., Mushagalusa, D., Katongo, C., Sibomana, C., Ajode, M. Z., Muderhwa, N., Smith, S., Ntakimazi, G., De Keyzer, E. L. R., Nahimana, D., Mulungula, P. M., Haambiya, L. H., Isumbisho, P. M., Limbu, P., Kimirei, I. A., Marwa, N. B., Mlingi, R. J., and Mangaza, A. M. 2023. Lake Tanganyika: Status, challenges, and opportunities for research collaborations. Journal of Great Lakes Research. 49 (6); 1-13.