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A strategy towards the “good”: a diagnosis of Lake Karla; Greece management practices during the last 20 years
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DOI：10.3389/fenvs.2026.1903658.png)
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Abstract
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IntroductionEutrophication and habitat loss are among the most pervasive threats to freshwater ecosystems globally; yet restoration outcomes for shallow Mediterranean lakes remain poorly documented and frequently inadequate. Lake Karla (Thessaly; Greece); historically one of the most ecologically significant wetlands in Greece; drained in 1962 and partially re‐established in 2010; offers a unique case to examine what prevents restoration success in a heavily modified; multi-purpose water body and what a new strategy must address. Although the Karla project was designed as a multi-service reservoir delivering irrigation; flood attenuation; and groundwater recharge; its ecological potential has been consistently assessed as Less than Good under the Water Framework Directive (WFD) since monitoring began in 2013.MethodsDrawing on official WFD lake monitoring data and published research datasets (physicochemical; nutrient; and biological quality elements); national River Basin Management Plans (RBMPs); and official technical records; we (a) diagnose the ecohydrological functioning of the lake and the pressures governing it; (b) review the effectiveness of past interventions against WFD ecological potential targets and management objectives across eight challenge areas; and (c) propose a function-based spatial ecological restoration strategy.ResultsOur analysis reveals a striking decoupling between total phosphorus (TP) reduction and biological recovery: the 2015–2020 decline in TP driven by improved Pinios River connectivity did not trigger ecological recovery — cyanobacterial dominance intensified and EQR values remained persistently poor. At the nutrient concentrations documented; neither nitrogen nor phosphorus approached genuinely limiting levels; and cyanobacterial dominance is driven by physical and biotic factors rather than nutrient stoichiometry. Application of a global eutrophication risk typology confirms that Lake Karla occupies Risk Type 4 — the highest category — combining high catchment nutrient delivery potential with extreme lake sensitivity. Engineering and hydrological objectives have been substantially met; ecological and water quality objectives have not.ConclusionThe root cause is a hierarchy of restoration priorities that placed irrigation and flood management above water quality and biodiversity. The proposed new strategy is organised around five spatially defined intervention zones spanning upland Natural Water Retention Measures; riparian buffer restoration; retrofitting of the artificial wetland; and in-lake biomanipulation; anchored within the restorative continuum framework and aligned with Nature Restoration Law obligations. Lake Karla’s trajectory offers a transferable diagnostic framework for reconstructed Mediterranean HMWBs where restoration priorities pre-dating the WFD placed water supply above ecological recovery.
Keywords:
eutrophication
catchment management
lake restoration
mediterranean lake
water framework directive
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