Lake Opeta

C(iii)Site contains nationally threatened or restricted habitat or vegetation types, AND/OR habitats that have severely declined in extent nationally

Lake Opeta qualifies as an IPA under sub-criterion C(iii) as one of the five best sites for nationally Vulnerable habitat freshwater marsh (VU). Encompassing 7.9% of the national resource, this IPA is possibly the largest extent of freshwater marsh national that could be managed as a single site. As freshwater wetlands become more threatened nationally, it is important to conserve the marshes at this site, particularly to preserve the many important ecosystems services they provide.

Lake Opeta IPA is one of the most important wetlands nationally. The lake and its surrounding habitats are situated in the Kyoga Basin in northeastern Uganda, in the districts of Nakapiripirit, Sironko, Katakwi and Kumi and is located 25 km north-west from Kumi town. The IPA boundary is based on that of Lake Opeta Wetland System Ramsar site, while the northern part of this IPA overlaps with Pian-Upe Wildlife Reserve. The main inflow into the Opeta system is through River Sironko (Kasangaki 2009).

Lake Opeta is one of the most important areas of freshwater marsh, a nationally Vulnerable habitat type, in Uganda. Encompassing 8% of the national resource (Richards et al. 2024), this IPA is likely the largest extent of freshwater marsh that can be managed as a single site. Wetlands are under significant pressure nationally and are estimated to have declined from 17.5% national coverage in the 1990s to 8.5% by 2021 (Wambede 2021). Several wetlands in Uganda have been heavily degraded due to agricultural encroachment, rice farming in particular, that result from land shortages (Bunyangha et al. 2022). Loss of ecosystem services has been linked to this encroachment, for instance around Mpologoma wetlands degradation has been linked to increased flooding locally (Wambede 2021). The Lake Opeta landscape also provides important habitat for Uganda’s only endemic bird species, Fox’s Weaver (Ploceus spekeoides). Conservation of the Lake Opeta Freshwater Marshes is, therefore, of great importance in order to avoid the loss of the numerous crucial ecosystem services provided by wetland habitats (see Key ecosystem services).

There is no IPA trigger species in Lake Opeta wetland system, however, further surveys may well reveal species of interest.

The main vegetation type of the general landscape in this area is Acacia - Hyparrhenia - Themeda grass savannah (Langdale-Brown et al. 1964). Lake Opeta wetland system lies on flat terrain and is predominantly an extensive marsh of Echinochloa pryamidalis and Vossia cuspidata surrounding the open water of the lake to the east and south graduating into dry Hyparrhenia grassland savannas. The swamp has Lake Opeta most of which is covered by Nymphea nouchali var. caerulea with Najas pectinata and Ceratophyllum dumersum and surrounded by a thin fringe or small pockets of Cyperus papyrus to the eastern side and patches of Miscanthus and Typha (Byaruhanga & Kigoolo 2005, Kalema 2005, Odull & Byaruhanga 2009). The marshy areas are fringed by seasonally flooded communities of impeded drainage with Panicum repens, Sporobolus pyramidalis, Cyperus articulatus C. denudatus and Cynodon dactylon (Kalema 2005). The drier land patches are composed of thicket and bushland communities of Euphorbia candelabrum, Grewia villosa in mixture with species of Acacia, Ziziphus, Combretum and Harrisonia.

In the centre of the IPA is Tisai Island, which is occupied by a small community of people. As a result, this area is largely transformed to arable agriculture (Google Earth 2023).

The climate of Lake Opeta wetland system is tropical in nature and is influenced by the air currents such as the southeast and northeast monsoons. The system has a rainy and dry season. The area generally experiences a uni-modal low rainfall which comes in the long, wet season of April to October, in contrast to the bimodal pattern of the south and west of Uganda (State of Environment Report, 1998). Rainfall is erratic, variable and highly localized, ranging from 500 – 1,000 mm with a mean annual figure of between 500 to 700 mm. Mean annual minimum temperatures range from 15 to 17.50 C and mean maximum temperature from 30 - 32.50 C.

Lake Opeta wetland system is underlain by a mixture of Pre-Cambrianand Cenozoic rocks of Pleistocene to recent (NEMA 2009). The rock types comprise the banded gneisses of Aruan tectonic Age (Byaruganga & Kigoloo 2005).

Lake Opeta Wetland is both an Important Bird Area (IBA) and a Ramsar Site (Odull & Byaruhanga 2009). NatureUganda has been promoting conservation of Lake Opeta as a potential tourism destination, and also prioritizing it for conservation because of its importance for survival of the Near Threatened Fox’s Weaver, Uganda’s only endemic bird (Byaruhanga & Kigolo 2005). This site is also of note for the presence of a Vulnerable cichlid fish, Paralabidochromis plagiodon, which is restricted to lakeshores of Lake Victoria, Kyoga and Opeta (FishBase 2024; Morris 2024).

NatureUganda has also been lobbying the relevant institutions to upgrade the conservation status of the area while the Wetland Management Department undertakes education and awareness activities in the area.

There is often overstocking of cattle grazing in the wetlands during dry seasons, which may have a long-term impact on the ecology and character of the area. Fishing occurs on the lake which results into cutting of trees for smoking the fish, as well as charcoal burning (Kalema 2005). River Sironko which drains into the Lake Opeta system, is highly turbid from agricultural activities upstream (Kasangaki 2009), which may well impact the quality of the freshwater marshes at this site.

Several important hydrological ecosystem services are provided by Lake Opeta and its wetlands. These include water storage, flood control, ground water recharge, sediment retention and water purification (Byaruhanga & Kigolo 2005). During the dry season, the wetlands provide a continuous discharge of water, maintaining water availability in the surrounding areas. The Lake Opeta area is used by the Iteso, Karimojong and the Pokot peoples for dry season grazing and watering of animals (Byaruhanga & Kigolo 2005). There is also a wooded island in the middle of the swamp called the Tisai which a small community occupies (Byaruhanga & Kigolo, 2005).

Alongside provision and regulation of hydrological services, parts of the site have been identified as a “probable peatland” in a national analysis of peat deposits (Elshehawi et al. 2019). If peat does underlie areas of this IPA, it would highlight its importance as a carbon store (although the wetland habitats likely store large amounts of carbon in any case).

Lake Opeta provides food, particularly a valuable source of protein, and livelihoods through fishing activities, with two landing sites on the lake (NaFIRRI 2008). It is likely that the freshwater marshes provide important nursery habitats for fish species at the site, including fish for catch and the threatened and restricted cichlid, Paralabidochromis plagiodon (VU).

Samuel Ojelel, Makerere University Herbarium

Sophie Richards, Royal Botanic Gardens, Kew

James Kalema, Makerere University Herbarium