# How blue is Bucharest?

Barely: 0.15% of the city's pixels are blue in the 22 August 2026 image. The lakes look green or dark teal; the blue identified on the map is on roofs and in swimming pools. The colour wheel shows the city in every other hue.

## Are Bucharest's lakes blue?

No, not in these ten images. On 22 August, lakes Floreasca, Tei, Plumbuita, Străulești and Pantelimon are green (hues from 131° to 141°). The closest to blue is Lake Morii: dark grey-teal, 184°. Hue is measured in degrees on the colour wheel: 0° red, 120° green, 240° pure blue; here, blue starts at 205°. The hue of the mean colour of none of these eight lakes goes above 184° in any image.
In the 3 February image, 91% of the city's pixels are classified as snow and the lakes look dark teal. The colour of water seen from space can be influenced by algae, sediment and depth; the table shows the hues in each image, not their cause.

## Where is the blue in Bucharest?

In small patches: inside the city boundary, no patch of blue pixels sharing an edge is larger than 0.87 hectares, and the largest is at the Valrom hall. As far as OpenStreetMap shows, the places below are a market, an industrial hall and apartment blocks, plus one swimming pool; the colour of roofs is read from the image. Turquoise (blue-green) is mostly found in one place: on 22 August, 72% of the city's turquoise pixels are in Lake Morii.
If every pixel where blue exceeds red (with blue-band reflectance above 0.04) is counted, the share rises to 7.3%. That total mostly consists of near-grey pixels and green or green-cyan ones (vegetation, bare ground, water) where blue is only slightly above red; only about 2.0% of these pixels are blue.

## Which sector has which colour?

Each cell shows the share of the sector's pixels whose hue is within 25° of the column's colour. Sector 1 has the highest share of green pixels (19%), Sector 5 the lowest (7.1%) and the highest share of orange (51%). In Sector 6, turquoise pixels are 5.5% of the total, mostly from Lake Morii.

## How it was measured

The image is a Sentinel-2 L2A scene from 22 August 2026 (tile 35TMK), cloud-free over the city. The displayed colour of a 10 × 10 m pixel is computed from the reflectance in the red, green and blue bands (B04, B03, B02): the value is multiplied by 2.8 and raised to the power 1/2.2 (an approximation of the sRGB gamma), in 8 bits. The map shows the same colours, and the percentages classify this rendering, not raw reflectance. Nine other scenes, from October 2025 to October 2026, are behind the date control.

A pixel “has the hue” of a colour if it lies within 25° of it on the hue circle (HSV model) and has a chroma of at least 0.05 (the gap between its largest and smallest RGB channel, on a 0 to 1 scale). For blue the window is 205°–255° (centre 230°); the thresholds are set on the displayed values and do not establish what a viewer calls blue. Near-grey pixels get no hue but stay in the total that shares are measured against. The city is the administrative boundary from OpenStreetMap (238.9 km², 2.39 million pixels); the sectors come from the same data.

In the 22 August 2026 image the blue share is 0.15%. Across five summer and autumn dates and three contrast stretches it stays between 0.13% and 0.21%; with the chroma threshold lowered to 0.02 it reaches 0.43%, and with a ±45° hue window instead of ±25° it reaches 0.61%. Dates with snow or cloud are left out. The results describe the images and settings checked; hues can vary with the date, the lighting and the surfaces observed.

At 10 m a pixel mixes roof, street and trees: small roofs do not show up separately and can be missing from the count. The places in the list were identified in OpenStreetMap by names and tags within 110 m of the colour patch; the patch itself is measured in the image.

## Sources

- Contains modified Copernicus Sentinel data 2025–2026. Sentinel-2 L2A, tile 35TMK, scenes S2B 22 August 2026 and nine others, via Earth Search and AWS Open Data. https://registry.opendata.aws/sentinel-2-cogs/
- European Space Agency: Sentinel-2 documentation and the scene classification (SCL). https://sentinels.copernicus.eu/web/sentinel/user-guides/sentinel-2-msi/product-types/level-2a
- © OpenStreetMap contributors, ODbL licence: city boundary, sectors, lakes, place names. https://www.openstreetmap.org/copyright