In short
- Streams (ρέματα) are protected by Law 4258/2014. Building within a demarcated stream's boundary lines is banned.
- Most streams have not been demarcated. A building permit near one then needs a provisional demarcation based on a 50-year flood study.
- Until a planned decree replaces them, buildings must keep at least 10 m from the flood lines inside town plans and settlements, and 20 m outside them.
- Official flood hazard maps cover designated high-risk zones only, for 50, 100 and 1000-year scenarios.
- Being in a mapped flood zone is not by itself a building ban, but it affects design, permits and insurance.
Streams in Greek law
Law 4258/2014 defines a stream (υδατόρεμα) as a natural or engineered channel that carries surface runoff. Irrigation and drainage ditches do not count. A stream's boundary lines (οριογραμμές) enclose its banks and its flood lines.
Demarcation (οριοθέτηση) is the procedure that fixes those lines, based on a topographic survey and hydraulic study, and it is published in the Government Gazette. Very small streams, with a catchment of up to 1 km² outside settlements or 0.5 km² inside them, normally do not need demarcation.
Building near a stream
- Inside a demarcated stream: the 2023 Building Regulation bans building within its boundary lines outright.
- Near a stream that is not demarcated: the building service can issue a provisional demarcation for a permit, based on a hydraulic study of the whole upstream catchment and flood lines for a 50-year return period. Building is allowed only outside those lines.
- Distances: until the decree provided for by Law 4067/2012 is issued, buildings must keep at least 10 m from each flood line inside town plans and settlements, and 20 m outside them.
In 2025 about 6,000 km of streams in flood-prone zones still had no demarcation, and a national project was contracted to demarcate them. For most plots, assume the stream near you has not been demarcated and ask your engineer.
Official flood maps
Under the EU Floods Directive, Greece maps flood hazard and flood risk for designated Areas of Potentially Significant Flood Risk (ΖΔΥΚΠ). The current Flood Risk Management Plans (second cycle) for all 14 river basin districts were approved in April to June 2025. Their hazard maps model 50, 100 and 1000-year floods and show extent, depth and velocity.
The maps are public on the Ministry of Environment's floods portal. The Ministry itself notes that they model a single synthetic rainfall event, so a real storm can flood differently. Work on the third cycle started in December 2025.
What a flood zone means for a buyer
There is no general rule that a mapped flood zone bans building. It does feed into the permit and design: floor levels, drainage and whether a hydraulic study is needed. It also matters for insurance. Since June 2025, businesses with turnover above €500,000 must insure against flood, earthquake and wildfire.
The bigger blind spot is outside the maps. Many small streams, gullies and local drainage paths are not modelled, and recent works such as culverts or road fills change how water moves. A site visit after heavy rain, and questions to neighbours, can tell you more than any map.
What a public-data pre-check shows
Every Core and Extended report checks the confirmed parcel against the official flood hazard and flood risk maps, at high and medium probability. The Extended report adds recorded historic flood events and the distance to mapped rivers and lakes. Each result comes with the questions to ask your engineer.
What it cannot tell you
It does not show stream boundary lines or whether a stream is demarcated, small streams that are not on the maps, or recent works. It is not a hydraulic study.
See a sample report →Questions for your lawyer or engineer
- 01Is there a stream, gully or dry bed on or near the plot, including small ones not on maps, and what is its catchment?
- 02Has it been demarcated, and if not, does a permit need a provisional demarcation with a 50-year hydraulic study?
- 03On a topographic survey, how far is the planned building from the flood lines and banks, and do the 10 m or 20 m distances affect it?
- 04Are existing buildings inside stream lines, and were they permitted or legalised?
- 05Is the plot in a mapped flood hazard zone, and what does that mean for floor levels, drainage and insurance?
Greek terms
| Greek | English | Meaning |
|---|---|---|
| Ρέμα / υδατόρεμα | Stream / watercourse | Channel that carries surface runoff, even if usually dry. |
| Οριοθέτηση | Demarcation | Official fixing of a stream's boundary lines. |
| Οριογραμμές | Boundary lines | Lines enclosing the banks and flood lines. |
| Προσωρινή οριοθέτηση | Provisional demarcation | Lines set for a building permit where no demarcation exists. |
| Περίοδος επαναφοράς | Return period | Average interval of a modelled flood, e.g. 100 years. |
| ΖΔΥΚΠ | Area of potentially significant flood risk | Zone covered by the official flood maps. |
| ΣΔΚΠ | Flood Risk Management Plan | River-basin plan that includes the flood maps. |