In 1961/2, the River Sateska was rerouted. Originally destined for the River Black Drim, its course was changed to enter Lake Ohrid to the west of Ohrid town. Running through agricultural and urban landscapes, it has since become a major source of pollution, trash, and sediment to Lake Ohrid, in certain seasons bringing up to 129 tonnes of suspended material (1). Daily.

After fifty years of this unwelcome input, the time has now come to return the Sateska home again…

Background 

Reflecting the very different environmental priorities of the last century, the Sateska was diverted for three reasons: A) to reduce the siltation of a reservoir along the Black Drim; B) to drain the Struga Marsh wetlands for agriculture; and C) to increase the hydroelectric potential of the lake (2). From deteriorating water quality to mismanagement of dams to the loss of bird habitat, all of these motivations have had negative influence on the ecology of the UNESCO Lake Ohrid region.

Some, however, may be reversible if the Sateska returns to its rightful place…

1961/2-Present

The above-mentioned 129 daily tonnes of suspended material are slowly creating an ecological black hole in the northern regions of Lake Ohrid’s world-unique ecosystem. After more than 5 decades, sediments from the Sateska now stretch 4 to 5 kilometers south from the river’s mouth and 1 to 1.5 kilometers east and west. They are even slowly building an artificial delta.

Alongside sedimentation is the nutrient load. Washoff from agriculture and wastewater from homes is accumulating eutrophication-causing phosphorous in the river water and dumping it into the lake. Eutrophication leads to a drop in the level of dissolved oxygen in the water, which makes it harder for certain species to survive and even for fish eggs to hatch (3).

Available data suggests that 39% of the phosphorous from all Lake Ohrid’s tributaries flows from the Sateska, making it the biggest individual source. Nitrogen triggers similar problems and the Sateska is the second-largest regional origin for that too (1).

Legacy

Non-natural eutrophication can be both ecologically devastating and hugely costly. It can create no-swim zones, impact drinking water, and decimate tourism receipts (4). It can trigger major shifts in ecosystem composition as well.

These worries are particularly acute for UNESCO Lake Ohrid. Although the water quality is generally still enviable, there are many signs that it is deteriorating. Moreover, a large portion of Lake Ohrid species are evolved to the location’s very specific high-oxygen waters. Small changes may catapult them towards extinction (3). And there is no replacement for many anywhere else on Earth.

The warning signs are growing. Endemic taxa are disappearing from areas around the mouths of Lake Ohrid’s tributaries (3); there are fears of a pollution gradient emerging from urban centers of the lake’s north (5); and a slide towards eutrophication has been recorded even stretching into deeper waters from the Sateska (6), which has also been identified as a source of non-native species (2).

The Future

In 2017, the UNESCO World Heritage Committee requested the Republic of Macedonia to explore options to make peace with the River Sateska and reunite its direct connection to the River Black Drim (7). Responding to this request, in a 2018 Progress Report to UNESCO, the Macedonian government acknowledged the Sateska’s negative impact, but has not yet offered any solution for how to ameliorate it (1).

The government is probably concerned by the potential costs and upheaval that re-rerouting the Sateska will cause. Ohrid SOS, however, believes that a greater worry is the cost, upheaval and irreversible loss that will ensue from leaving it where it is…

References

(1) National Commission of UNESCO for the Republic of Macedonia (2018) Progress Report on the Implementation of the Recommendations according to the World Heritage Committee Decision 41 COM 7B.34.

(2) The World Heritage Centre/ICOMOS/IUCN (2017) Mission Report: Joint World Heritage Centre/ICOMOS/IUCN Reactive Monitoring Mission to the World Heritage property, Natural and Cultural Heritage of the Ohrid Region (the former Yugoslav Republic of Macedonia).

(3) Matzinger, A and Veljanoska-Sarafiloska, V. (2004) Lake Ohrid – A Unique Ecosystem Endangered By Eutrophication? BALWOIS 2004, Ohrid, Macedonia, 25-29 May 2004.

(4) Dodds, W. K., W. W. Bouska, J. L. Eitzmann, T. J. Pilger, K. L. Pitts, A. J. Riley, J. T. Schloesser, and D. J. Thornbrugh. (2009) Eutrophication of US Freshwaters: Analysis of Potential Economic Damages. Environmental Science and Technology 43 (1).

(5) Jordanova, M., K. Rebok and E. Rocha. (2016) Liver pathology of female Ohrid trout (Salmo letnica Kar.) from the eastern coast of Lake Ohrid: baseline data suggesting the presence of a pollution gradient. Turkish Journal of Fisheries and Aquatic Sciences 16:241-250.

(6) Trajanovska, S., Talevska, M., Imeri, A., and Schneider, S. C. (2014) Assessment of littoral eutrophication in Lake Ohrid by submerged macrophytes. Biologia 69(6):756-764.

(7) World Heritage Committee Decision: 41 COM 7B.34.