As you travel around the sweeping coastline of St Brides Bay you’ll easily spot the white flank of Grassholm Island on the western horizon.

Seasonal visitors will notice that the island seems to be whiter in summer and you’d be forgiven for thinking it might have snowed!

The island turns white when 39,000 pairs of breeding North Atlantic gannets come here every year to rear their young. This is the third largest gannet colony in the UK, supporting around 10% of the entire world gannet population.

Grassholm Island is a spectacular sight, sitting 11-miles off the St Davids coastline, and is easily reach by boat trip. Your day starts with a boat brief before an exhilarating boat journey through Ramsey Sound – perfect for blowing off the cobwebs first thing in the morning!

All boat trips have knowledgeable staff, who are quick to read the landscape and share information about the waters, islands, bird and marine mammal wildlife that you will be looking at along your journey.

As the boat circles, the island hundreds of gannets launch into flight, revealing even greater numbers of birds and nests on the western side of the rock.

Gannets are large birds. Their wingspan can reach up to 2 meters and watching them dive from 30 meters into the water, travelling at speeds upto 60mph, is a spectacular sight. Especially up close!

You’ll quickly be invited to keep your eye on the horizon for splashes of water indicating the second thing everyone hopes to see on this trip – porpoise!

As you race out to the island you might see rafts of puffins and gliding Manx shearwaters as well as porpoise, grey seal and possibly a glimpse of a larger marine mammal like the common dolphin or Risso’s dolphin.

Once at the island your attention will turn to the majestic gannet. The colony is at its busiest and noisiest in the summer, with breeding gannets constantly coming and going with fish for their chicks, while thousands of non-breeders gather to socialise.

If the weather permits you’ll travel further west towards The Smalls – a cluster of rocks 20 miles out to sea housing one of the remotest lighthouses in the UK and the last piece of landmass before America.

Spending time on the water, observing the marine wildlife of Pembrokeshire in their natural habitat is one of the most memorable things you can do in Pembrokeshire this summer. What a treat.

Grassholm is a RSPB sanctuary reserve with a strict ‘no landing’ policy.

Boat trips to Grassholm Island are available from Martins Haven with Pembrokeshire Islands, or with Falcon Boats, Thousand Islands and Voyages of Discovery from St Justinians.