Water levels in northern Greece’s lakes decline
Intensive agriculture, climate change and mismanagement threaten the future of Macedonia’s meres and their ecosystems
It is widely believed that northern Greece is rich in water resources, but the reality is quite different. A steady decline in water levels has been recorded across all large and small lakes in the region. In fact, the lakes of Macedonia are at their lowest levels since 2013. This reduction in water reserves, as expected, increases the pressure on already strained ecosystems. Interestingly, Greece’s artificial lakes are in better condition than its natural ones.
Data on the quantitative and qualitative status of the lakes are collected on behalf of the Ministry of Environment by the Greek Biotope / Wetland Center (EKBY) of the Goulandris Natural History Museum. EKBY has been managing this project since 2012, starting with 53 monitoring stations, which increased to 80 in 2021 with the addition of lakes from mainland Greece, the Aegean islands and Crete. A total of 74 lakes are now monitored. Most lakes in Central and Western Macedonia have been monitored since 2012, providing over a decade’s worth of data on their quantitative and qualitative fluctuations.
According to EKBY’s measurements, the water levels of the four natural lakes in Central Macedonia (Volvi, Koroneia, Doirani and Pikrolimni) have remained at low levels since 2013. The lowest levels were recorded between 2013 and early 2014, with lakes Koroneia, Doirani and Pikrolimni hitting their lowest points during that time.
“From 2016 until 2019, there was a downward trend in these four lakes. That year, Volvi reached its lowest level in the past 12 years,” explains Dimitris Papadimos, head of the water and soil resources department at EKBY.
“From 2020 to August 2024, the average levels of lakes Volvi and Koroneia appear to have stabilized at 35.8 meters and 70.3 meters, with a maximum fluctuation of 1.3 meters and 1 meter, respectively, depending on the pattern of annual rainfall. Since 2020, the level of Pikrolimni has again dropped below 44 meters, before its significant rise in 2015, frequently even drying up, as it did this summer.”
‘Large-scale disturbances caused by human activity, such as water extraction and energy production, particularly amid climate change, negatively affect ecosystems’
A drop of just a few centimeters in water level can translate into millions of cubic meters of lost water. “For example, in Lake Kastoria, a 0.20-meter drop in the water level since 2018 means that the lake has lost 6 million cubic meters of water.”
The fluctuation of lake levels is, of course, a natural phenomenon, as long as it does not seriously disrupt the ecosystem. “In Mediterranean lakes, seasonal water level fluctuations are common due to the climate. These are natural disturbances, and many studies suggest that a certain level of disturbance, both in magnitude and frequency, is often beneficial for maintaining high biodiversity,” explains Papadimos. “However, large-scale disturbances caused by human activity, such as water extraction and energy production, particularly in the context of climate change, negatively affect ecosystems.”
A key requirement for maintaining lake biodiversity and ensuring that lakes can provide essential services (e.g., fish for food, water for drinking and irrigation) is the maintenance of a minimum water level, known as the “ecological level.” In 2016, EKBY launched a research project (in collaboration with the Water Directorate of East Macedonia & Thrace, the Aristotle University of Thessaloniki, the Institute of Fisheries Research [IFR] of ELGO-Dimitra, and the Norwegian Institute of Bioeconomy Research) to determine the minimum required levels for water bodies. This project explored the ecological needs of fish populations and aquatic vegetation in relation to water levels, along with the lakes’ morphological characteristics and historical water level data in four natural lakes in Western Macedonia (Zazari, Cheimaditida, Petron and Vegoritida).
Eight years after proposing ecological water levels for the four natural lakes, many valuable conclusions have emerged. “It can be observed that in lakes near areas of intensive irrigated agriculture, such as Cheimaditida, or in basins where large-scale irrigation occurs, like Petron and Vegoritida, water levels have dropped since 2019, and their annual fluctuations are lower than in the past. This adverse condition appears to be linked to both a reduction in rainfall and rising regional temperatures, as well as current management practices related to irrigation,” explains Papadimos. “It is therefore crucial to monitor these ecosystems and the long-term impacts of hydrological pressures on biodiversity, especially as the strain on lake levels is expected to worsen with climate change.”
Lake Zazari, in particular, has yielded alarming findings. Based on current conditions and future projections using climate models, scientists estimate that the amount of water entering the lake will drop by half, falling from 5.7 million cubic meters to just 2-2.6 million cubic meters annually. “This decrease will reduce the lake’s water renewal rate, with negative consequences for water quality,” says Papadimos. “Similar reductions are seen in the lake’s outflows to downstream ecosystems, which rely on Zazari’s overflow. This diminished flow will severely affect Lake Cheimaditida, which depends heavily on this source. To maintain current irrigation levels, the area available for irrigation would need to be reduced by over half, between 54% and 64%.”
Falling lake levels have significant ecological consequences. “Northern Greece’s lakes are not in optimal chemical or ecological condition,” explains Vasso Tsiaousi, coordinator of EKBY’s lake monitoring network. “Artificial lakes are generally in better shape than natural ones because they are often located in remote, forested areas, and the reservoirs are protected from human pressures. Greece has already faced the European Court of Justice (ECJ) due to the condition of Lake Koroneia, while lakes such as Volvi, Kastoria and Vegoritida are also classified as being in moderate condition.”
A major factor affecting water quality in these lakes is eutrophication. “Eutrophication usually results from pollution sources, such as phosphorus from fertilizers or urban wastewater. This leads to changes in the composition of aquatic communities, with more resilient species dominating. In extreme cases, aquatic vegetation can be destroyed.” Water extraction for irrigation also adds significant pressure. “As a Mediterranean country, rising temperatures will further reduce the available water for irrigation. We must address this, as lake water resources are finite.”
Papadimos emphasizes that, given the pressure from drought and increasing temperatures, immediate action is required. “Reducing irrigated areas significantly impacts local communities, so it cannot be our first step. Our priority should be to reduce water losses from irrigation networks, as large amounts of water are currently wasted. Secondly, we should focus on changing irrigation techniques and crop selection. Only after these steps are exhausted should we consider reducing the area of irrigated land.”
