The 2013 heatwave in the United Kingdom and Ireland was a period of unusually hot weather primarily in July 2013, with isolated warm days in June and August.
A prolonged high pressure system over Great Britain and Ireland caused higher than average temperatures for 19 consecutive days in July, reaching 33.5 °C (92.3 °F) at Heathrow and Northolt.
[9] The heatwave ended on 23 July with heavy thunderstorms, bringing flooding and lightning strikes that caused delays on motorways and railways, power cuts and fires.
On 18 July, the London School of Hygiene and Tropical Medicine reported that the first 9 days of the heat wave had caused up to an additional 760 deaths in the UK.
[19] The death of thousands of fish in rivers and lakes was attributed to the elevated temperatures lowering the amount of oxygen in the water to toxic levels.