Mayfly main hatch

Window

Typical: 25 May – 15 Jun (2026)

Water temp trigger

~14.0°C

Latitude range

50-52°N

Duffer's Fortnight. Hawthorn blossom is a useful three-week-out warning.

Relevance to fishing

The classic 'Duffer's Fortnight'. Every fish in the river feeds, even big chub and pike take fry on. The signal trout event of the year.

Phenology chain

Triggered by

• Hawthorn (May) blossom typically 21d before (range 14 – 35d)
• Swifts arrive typically 21d before (range 14 – 30d)

Triggers

• Tench spawning typically 14d after (range 7 – 28d)