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| The floodplain of the Rafina Megalo Rema stream; looking upstream. The trees punctuating the green thickets of Reed Cane and rushbeds are nearly all Salix alba, a rare riparian woodland stand for Attika (drone photo from: https://megalorema.gr/). |
Petreza: The Floodplain Attica Cannot Afford to Lose
Hidden between the towns of Spata and Pikermi, remains one of the last free-flowing streams in Attica. This is the main stem of the Rafina Megalo Rema, as if flows through part of the Mesogeia Plain, this is the Petreza floodplain.
Along the river's main channel, as it exits the entrenched reach of the Attiki Odos Highway, lies Petreza, one of the region's last natural river floodplains and arguably one of the most valuable yet overlooked landscapes for nature conservation in the Athens Metropolitan Area. Far more than a rare patch of open green space, Petreza is a living ecosystem that supports exceptional biodiversity. Although parts of the area may benefit from legal protection (on paper that is...), this unique floodplain is now under imminent threat from a large-scale river engineering project that proposes to transform much of the natural river into a heavily channelized flood-control corridor. The project, costing just over 100 million Euros is now underway - buldozers tearing down trees... If implemented in its totality, the project could irreversibly alter one of Attica's last functioning river ecosystem landscapes.
Floodplains are the areas where rivers naturally expand during periods of high flow. Rather than being "unused land", they act as natural reservoirs, slowing floodwaters, storing carbon, filtering pollutants and recharging groundwater. Across Europe, scientists increasingly recognise that protecting and restoring floodplains is among the most effective and cost-efficient ways of reducing flood risk while simultaneously conserving biodiversity.
The Petreza reach represents one of the largest remaining floodplain systems of the Rafina Megalo Rema, one of the few largely free-flowing rivers left in the Athens Metropolitan Aegion. Its riparian woods, wetlands and seasonally flooded habitats support remarkable wildlife, including around 150 recorded bird species, numerous freshwater fish, including lots of European Eels (Critically Endangered!), amphibians, reptiles (a populations of Stripe-necked Terrapins) and a museum-full of aquatic invertebrates. Several habitat types found here, including white willow (Salix alba) riparian woods mixed with rush beds (Juncus spp), are now exceptionally rare in Attica.
Beyond its ecological importance, Petreza provides essential ecosystem services for people. By remaining connected to the river, the floodplain naturally attenuates flood peaks before water reaches downstream urban areas. It also improves water quality, supports groundwater recharge and contributes to local climate regulation during increasingly frequent heatwaves. These benefits are precisely why the European Union now promotes Nature-based Solutions as a cornerstone of modern water management.
Today, however, Petreza is a battle ground between the government-promoted project for flood control and environmentalists, including concerned scientists. My colleagues at HCMR have written technical letters asking for this project to stop. It must be re-designed as a Nature based Solutions project that will protect key natural areas such as Petreza. The conflict is over design and implementation of the proper flood-control infrastructure, we are not against a project, we strongly disagree with the kind of project. Scientists have expressed concern that disconnecting the river from its floodplain, removing riparian vegetation and replacing natural riverbanks with hard engineering structures (gabion held levees) will totally degrade ecosystem functioning, reduce biodiversity and compromise many of the ecosystem services that make the floodplain valuable. Instead of eliminating floodplains, current European practice increasingly favours working with natural river processes rather than against them. So our Greek project is anachronistic, poorly planned, haphazard, and plain stupid!
The choice facing Petreza - and the Greek Government agencies that support this- is therefore much larger than a local planning issue. It reflects two contrasting approaches to flood management: one based primarily on traditional high-cost engineered channels, and another that combines flood protection with ecosystem conservation through Nature-based Solutions.
As climate change brings more intense rainfall and hotter summers to the Mediterranean, preserving natural floodplains like Petreza is becoming not only an environmental priority but also an investment in public safety and long-term resilience. Once these ecosystems are lost, they are extraordinarily difficult—and often impossible—to restore.
Saving Petreza means protecting one of Attica's last living river landscapes, ensuring that future generations inherit a river capable of supporting both nature and people.
After more than 30 years working in river and wetland conservation, I am convinced this project could have been designed very differently. Destroying one of Attica's last natural floodplains is a choice—not a necessity.
Visit the environmentalists website to find out more (https://megalorema.gr/).
We at HCMR (Inland Waters) support the environmental campaign to STOP the engineering project under way on the Rafina Megalo Rema Stream.
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| The upper Petreza floodplain, looking upstream from a drone image in early spring. Newly leafed white willow (Salix alba) line the anastomosing stream banks, while extensive seasonally flooded rush meadows stretch beyond the stream banks in the floodplain. This exceptional mosaic of riparian woodland and wet meadow habitats is unique and survives here on a scale found nowhere else in the peninsula of Attika (drone photo by the Author). |
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| The upper part of the Petreza floodplain; drone photo looking upstream. Early spring photo shoing recently leaved Salix alba (green trees) and the extensive high thickets of reed cane (drone photo by the Author). |
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| The lower, last part of the Petreza reach near the Arionos Bridge, here looking down-river towards the Arionos road and the eventual confluence of the main-stem with the Valanaris tributary (drone photo by the Author). |
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| The lower, last part of the Petreza reach near the Arionos Bridge, here the river enters a shallow valley, in the distance the Etos Hill (drone photo by the Author). |
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| Walking along the river after flood waters enter the fields and rushbeds. Photo: late May 2026. |
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| Much of the Petreza reach is thick with these towering reed cane thickets (Arundo donax). Photo: late May 2026. |
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| In late spring the walk on the small road along the right side of the Petreza reach is wonderful. A naturalists paradise. Photo: late May 2026. |
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| The Petreza is an important hotspot for birdlife; being located right next the the Loutros Spata hotspot it hosts well over 150 bird species, including many rare migrants. One the threatened migrants is this Turtle Dove. Photo: late May 2026. |
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| Fish abound in most parts of the Petreza reach of the river especially in the upper and mid floodplain areas. Eels are very common and they probably feed on these small schooling fishes; these being Rhodes Minnows (Ladigesocypris ghigii), translocated from Rhodes and now well established. Photo by Antonis Lazaris. |
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| We know very little about the biodiversity of this area. One of Antonis Lazaris's students documented the existance of the Stripe-necked terrapin in the stream at the Petreza floodplain. |
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| The catchment of the river basin of the Rafina Megalo Rema stream. In red outline the main-stem strech known as the Petreza reach where the exceptional floodplain habitats are located (base-map from Karymbalis et al. 2021). |
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| Location map of the Petreza Flood plain area (map: sketch deliniation by S. Zogaris on recent Goole Earth images). |
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| A map of protected area designations in the immediate area. The yellow zone is Zone B2 of Moderate Protection of Landscapes and Archeological Sites (Z.O.E. Mesogeion). Part of the floodplain of Petreza is within this designation. |
Resources
https://megalorema.gr/en/rafinas-great-river/
Karymbalis, E., Andreou, M., Batzakis, D.-V., Tsanakas, K., & Karalis, S. (2021). Integration of GIS-Based Multicriteria Decision Analysis and Analytic Hierarchy Process for Flood-Hazard Assessment in the Megalo Rema River Catchment (East Attica, Greece). Sustainability, 13(18), 10232. https://doi.org/10.3390/su131810232
European Environment Agency (2019). Floodplains: a natural system to preserve and restore. EEA Report No. 24/2019.
European Commission Joint Research Centre. Nature-based Solutions for Water Management.
Penning, E. et al. (2023). Nature-based solutions for floods, droughts and biodiversity: Do we have sufficient proof of their functioning? Cambridge Prisms: Water.
Papadaki, C., Dimitriou, E., Skoulikidis, N. et al. (2023). Regarding the river engineering project being implemented at Rafina Megalo Rema stream. Hellenic Centre for Marine Research.https://www.researchgate.net/publication/385420330_Regarding_the_river_engineering_project_being_implemented_at_Rafina_Megalo_Rema_stream_in_Greek
HCMR (2019). Report on Biodiversity in Water Bodies and the Wider Riparian Area of the Megalo Rema Rafina (Attica).
Zogaris S, Charmpila EA, Vukić J, Giakoumi S, Barbieri R, Zogaris D, Ašenbrenerová E, Viñuela Rodríguez N, Tarkan AS and Šanda R. 2023. Unnoticed introductions, a silent threat for biodiversity: island endemic Ladigesocypris ghigii (Actinopterygii, Leuciscidae) translocated to continental Greece. The European Zoological Journal, 90(2), pp.840-855.
