The Pátka Reservoir was last in a proper condition more than 10 years ago
The Pátka Reservoir, which has played a key role in replenishing Lake Velence for decades, has faced severe ecological challenges in recent years. In their most recent study, a team led by Dr. Enikő Magyari, Professor at ELTE’s Department of Environmental and Landscape Geography, used modern paleoecological and geochemical methods to shed light on the reservoir’s past. The researchers aimed to understand what lies behind the drastic decline in water quality and what can be done to save the reservoir. Their new paper, published in the prestigious journal Hydrobiologia, focused on investigating the ecological transformation of the reservoir over the past four decades.
Sediment sectioning
A research group formed within the National Laboratory for Climate Change reconstructed the reservoir’s condition from the 1980s to the present by analyzing a 54 cm-long sediment core taken from the reservoir, in order to understand the processes that led to the deterioration of water quality.
Enikő Magyari with the sediment core sample
Based on chironomid (non-biting midge) remains, pollen preserved in the sediment, and a comprehensive geochemical analysis, they identified three clearly distinct periods:
- 1983–1997: An unstable period following the creation of the reservoir, disrupted in the early 1990s by drainage and later refilling. Opportunistic chironomids (species of Chironomus) indicating low-oxygen conditions dominated the sediment record. High sediment input and low biological productivity were characteristic.
- 1997–2015 (reference condition): This was the reservoir’s “golden age.” In this mesotrophic water body, a stable water level enabled the development of abundant submerged macrophyte vegetation and improved oxygen conditions in bottom waters. More sensitive fauna elements associated with macrophytes (e.g., Cladotanytarsus species) appeared, and ecological diversity increased. Paleoecological and geochemical data consistently indicated that this was the reservoir’s most favorable ecological state. It was characterized by moderate nutrient loading, aquatic vegetation, stable sediment accumulation, and balanced benthic communities. The researchers designated this period as the official reference condition for restoration.
- 2015–2022: In the youngest sediment layers, the team observed a rapid decline in water quality and a drastic increase in organic matter content (TOC, TbN, TS), during which the reservoir shifted to an oxygen-depleted, hypertrophic state. This was also confirmed by the return of Chironomus dominance. Mass fish kills and the loss of the reservoir’s water-supply function led to the reservoir being drained in 2024.
“The results indicate that the deterioration of water quality may be driven not by agricultural activity in surrounding areas, but primarily by fisheries management within the reservoir (intensive feeding and fish stocking), as well as nutrient inputs from inflowing waters,” - highlighted by Eszter Tombor, PhD student and first author of the paper. - “The causes are strongly linked to global climate change, which has resulted in increasingly extreme precipitation patterns in the region.”
Eszter Tombor, a PhD student, during field sampling
These negative impacts are compounded by the diversion of the Császárvíz stream—the reservoir’s main inflow—along its upper reach, meaning that today a high proportion of treated municipal wastewater is present in the streambed.
In light of their findings, the authors emphasized that ecological rehabilitation of the Pátka Reservoir is essential to ensure the safe replenishment of Lake Velence. Proposed measures include carefully planned dredging, regulating angling activity, increasing the proportion of predatory fish, and improving the water quality of the Császárvíz stream, so that the reservoir can once again achieve the stable, healthy condition observed between 1997 and 2015.
Further details can be found in our published paper:
Tombor, E., Korponai, J.L., Zsigmond, AR. et al. Response of a shallow water reservoir to anthropogenic stressors: implications for the water supply of lake velence, a major recreational lake in Hungary. Hydrobiologia (2026).