The tide travels around Ireland
The Atlantic tide arrives at the south-west corner of Ireland first. From there it splits: one arm runs up the west coast past Galway, Mayo and Donegal, the other works east along the Cork and Waterford coast and then north through the Irish Sea. The two arms meet again off the north coast. That is why Castletownbere and Malin Head, at opposite ends of the country, have high water at almost the same time, while Dublin, sitting halfway along the Irish Sea arm, is several hours later.
The Irish Sea has a twist of its own. Tidal waves entering from the south (through St George’s Channel) and from the north (through the North Channel) meet near Arklow and Wicklow. Where they meet, the range almost cancels: Arklow and Rosslare have some of the smallest tides in the country, under 2 m at springs, while Dublin Bay 60 km north sees 4 m.
West coast ranges are big
Galway Bay, the Shannon estuary and Clew Bay all see ranges over 5 m on the largest springs. Beaches there dry out for hundreds of metres, and the flood comes back quickly across flat sand. On the east coast the same beach might show 2 m of range and change far less through the day.
Best times for swimming, walking and fishing
Swimmers on a shelving beach usually want the hour either side of high water, when the water is deep close in and you are not wading out over 100 m of sand. At steep-to spots such as harbour steps or the Forty Foot, mid tide to high tide is safest because the ladder still reaches the water.
Walkers, rock poolers and dog owners want low water. Aim to arrive an hour before the predicted low, which gives you two hours of falling and slack water before the flood starts to come back in. On sand flats and around tidal islands the flood can return faster than walking pace, so know your low water time before you set off.
Shore anglers generally fish the last two hours of the flood and the first hour of the ebb. Boat owners need the height as much as the time: a slip that dries at 1.0 m is unusable at a 0.6 m low.
Where the tide differs most: county by county
Dublin Bay dries a kilometre out at spring lows and floods back faster than walking pace on the Bull Island flats. Wicklow and Wexford have the smallest ranges in the country and the fastest tidal streams off the headlands. Cork Harbour is sheltered inside but runs hard at Roches Point. Kerry and Clare face the open Atlantic with ranges near 5 m on the Shannon. Galway Bay has the largest range on the west coast and the tidal causeways of Connemara catch cars every year. Mayo, Sligo and Donegal mix surf beaches with deep, sheltered bays where high water lags the nearest gauge by 20 minutes or more. Each county page explains the local pattern in more detail: Cork, Donegal, Galway, Dublin, Mayo, Clare, Wicklow, Kerry, Waterford, Wexford, Louth and Sligo.