Data story
Coral heat stress at 1,193 of the world's dive sites
Using NOAA Coral Reef Watch data (as of May 2026), we scored heat stress at every reef dive site in the OpenWaterAtlas database. 422 sites (35%) are under coral heat stress, 81 at a level where bleaching is likely, and 43 at the severe level where coral mortality is expected. The hardest-hit dive destination is Ecuador, where all 9 tracked sites sit at severe stress (mean 15.6 Degree Heating Weeks — anything over 8 signals likely mortality).
Dive destinations ranked by coral heat stress
Countries with 5+ tracked reef dive sites, ordered by mean Degree Heating Weeks (DHW). DHW ≥ 4 = bleaching likely; ≥ 8 = mortality likely.
| Destination | Sites | Mean DHW | Under stress | Severe | Status |
|---|---|---|---|---|---|
| Ecuador | 9 | 15.6 | 9 | 9 | Severe |
| Costa Rica | 6 | 8.2 | 6 | 5 | Severe |
| Brazil | 9 | 4.1 | 8 | 1 | Severe |
| Colombia | 68 | 3.5 | 28 | 28 | Severe |
| Madagascar | 7 | 3.2 | 7 | — | Heat stress |
| Australia | 45 | 2.5 | 34 | — | Heat stress |
| Thailand | 63 | 2.4 | 41 | — | Heat stress |
| Maldives | 147 | 1.8 | 139 | — | Heat stress |
| Indonesia | 289 | 1.3 | 145 | — | Heat stress |
| France | 51 | 0.1 | 1 | — | Heat stress |
| Egypt | 224 | 0 | 0 | — | No stress |
| Cyprus | 11 | 0 | 0 | — | No stress |
| Mexico | 32 | 0 | 0 | — | No stress |
| Dominican Republic | 7 | 0 | 0 | — | No stress |
| Jordan | 7 | 0 | 0 | — | No stress |
| Spain | 10 | 0 | 0 | — | No stress |
| Philippines | 106 | 0 | 0 | — | No stress |
| Japan | 26 | 0 | 0 | — | No stress |
| Oman | 5 | 0 | 0 | — | No stress |
| United States | 38 | 0 | 0 | — | No stress |
| Cape Verde | 6 | 0 | 0 | — | No stress |
Method & data
Each dive site is matched to its nearest NOAA Coral Reef Watch 5 km grid cell, from which we read the Degree Heating Weeks (DHW) — the accumulated thermal stress over the trailing 12 weeks. DHW is the standard NOAA metric: 0 = no stress, ≥ 4 = significant bleaching likely, ≥ 8 = severe bleaching and mortality likely. Cold-water destinations (e.g. Norway, the UK) show no stress and are excluded from the reef ranking. The full spot-level table is part of our open dataset (CC-BY 4.0 on Zenodo), so anyone can reproduce or extend this analysis.
Source: NOAA Coral Reef Watch (public domain). Reef site data: OpenWaterAtlas open dataset. Reading as of May 2026.
Planning a trip? See when each reef is best to dive on the best-time-to-dive calendar, or browse conditions for any site in the dive atlas.