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Coral reefs seen from space, 1985–2026

Every reef, every day

Each row below is one of the 214 coral-reef regions that NOAA's Coral Reef Watch follows by satellite, from the northernmost at the top to the southernmost at the bottom. Each column is a week, from January 1985 to November 2026. Orange means heat at which corals are likely to bleach; red and darker, heat at which some are likely to die.

No stress or watchWarningAlert 1: bleachingAlert 2: some deathsAlert 3Alert 4Alert 5No dataTap or click a row to open that region below. Grey: before the record starts.

Four waves of heat, and one much wider

Corals live in a narrow band of temperature. When the sea stays too warm for weeks, they expel the algae that live in their tissue and give them food and colour. They turn white, and if the heat lasts, many die. Coral Reef Watch measures this heat in degree heating weeks: how far, and for how long, the sea has stayed above the warmest normal month in the last twelve weeks.

The record shows the four global bleaching events: 1998, 2010, 2014 to 2017, and 2023 to 2025. Counted by region, the last was by far the widest. In 1998, 45 of the 214 regions reached Alert Level 2, the heat at which some corals are likely to die. In 2010, 85. In 2016, 103. In 2024, 171. Since January 2023, 197 of the 214 have reached it at least once.

In June 2026 NOAA said the global event had probably ended in mid-2025. But heat is still arriving region by region: by 11 November 2026, 101 regions had reached Alert Level 2 this year, as many as in all of 2025.

Share of regions under bleaching heat, week by week

The reef you swam over

Pick a region: search by name, choose a holiday coast below, or tap a dot on the map. Each row of its calendar is a year, each column a day.

    What the colours mean, and what they do not

    Alert Level 1 (at least 4 degree heating weeks): bleaching across the reef is likely. Alert Level 2 (8): bleaching with deaths of the corals most sensitive to heat. Levels 3, 4 and 5 (12, 16 and 20) mean deaths across many species, then more than half, then more than 80 percent of corals. These are risks the heat makes likely. Whether corals actually bleached or died is found by divers, not satellites.

    Each region is a stretch of sea around reefs, made of 5-kilometre squares. For each day NOAA takes a hot spot within the region, the 90th percentile, so the colour describes the hotter parts, not every reef in it. NOAA's own figure for the 2023–2025 event, 84 percent of the world's reef area, is counted by area, not by region, so it is not the same measure as the counts above. Each colour is the highest level in the seven days to that date, so weeks are counted here rather than days.

    Send it on

    Find the reef you swam over, and see what the last three years did to it.

    Sources

    All of the data comes from NOAA Coral Reef Watch, downloaded on 13 November 2026.

    1. NOAA Coral Reef Watch, Version 3.1 daily 5 km satellite regional virtual station time series, 1985 to 11 November 2026, all 214 stations, accessed 13 November 2026. Public domain.
    2. NOAA Coral Reef Watch, virtual station description (the 90th-percentile HotSpot of each region, the alert codes, Alert Levels 3–5 added to the station files on 2 November 2026, across the whole record) and methodology (HotSpot, Degree Heating Weeks over 84 days, CoralTemp v3.1 at about 5 km).
    3. NOAA Coral Reef Watch, alert levels and their potential impacts.
    4. NOAA Coral Reef Watch, fourth global coral bleaching event: confirmed 15 April 2024; about 84.4% of the world's reef area under bleaching-level heat stress from 1 January 2023 to 30 September 2025; mass bleaching in at least 83 countries and territories; earlier events 1998, 2010 and 2014–2017 (68.2%).
    5. NOAA NESDIS, World's fourth mass coral bleaching event likely ended in 2025 (2 June 2026).
    6. Map: NASA Blue Marble (public domain).