North Sea reaches warmest temperature ever recorded in Dutch waters

The North Sea reached a record-high average temperature of 21.5 degrees over the weekend, according to the KNMI. Records dating back to 1984 show that the water has never been this warm. The KNMI attributed the unusually high temperatures to climate change combined with a high-pressure system that brought sunny, calm weather.

The record was measured at the Goeree Light Island, a monitoring platform located roughly 30 kilometers off the coast of Hoek van Holland.

The previous North Sea temperature record was set in August 2018, when the water averaged 21.4 degrees. KNMI expects new records to follow as global warming continues, warning of consequences including rising sea levels, more heat and drought, and heavier rainfall. The institute is urging further reductions in greenhouse gas emissions.

The North Sea has recorded temperatures above 20 degrees on 35 days so far this year. That puts 2026 on track to challenge the record set in 2022, when the water surpassed 20 degrees on 43 days.

This absolute peak is the culmination of an ongoing marine heatwave. The current continuous heatwave in the North Sea began back on May 24. A marine heatwave is officially declared when sea temperatures stay significantly above normal for at least 5 consecutive days. The previous record for the longest continuous North Sea heatwave was just 27 days.

The prolonged marine heatwave threatens local marine life with mass mortality events affecting colder-water fish, algae, seaweed, and commercial blue mussel populations.

Hotter sea surface temperatures drastically increase local humidity and overnight coastal temperatures. This creates a volatile atmospheric baseline that fuels intense convective rainstorms and flash flooding along the Dutch and Belgian coastlines during autumn.