It may be the jewel of the county's coast but even on a sweltering summer day, the grey waters off Cromer beach can seem a little uninviting.

This summer, however, visitors have been struck by the sea's stunning colours, which give more than a hint of the Caribbean to this most Norfolk of resorts.

Rocks are being used as part of the new sea defences (Image: Phillip Corbett) Rather than the usual dark tones of the North Sea, the shallows along the beach, especially around the pier, are showing a dazzling array of azure blue and turquoise.

Officials at North Norfolk District Council have now revealed the reasons for this remarkable transformation - ongoing work to improve the resort's sea defences.

Cromer Pier (Image: Phillip Corbett) As part of the £25m project workers are excavating into the sea bed below the beach and exposing a layer of chalk sediment which is affecting the colour of the waters above.

'I'VE NEVER SEEN THE WATER LIKE THIS BEFORE'

Among those taken aback by the town's new, azure waters was Suzanne Allsopp-Franklin, who took photographs of the sea while visiting for the day with her family.

"The water looked amazing that day, so beautiful and nothing like how I had seen it before," she said.

Sea defence works are taking place near the pier (Image: Joanna Durndell) Joanna Durndell was also struck by the colours during her recent visit.

"I spent a lot of time there with my grandparents as a child and have never seen the sea such a rare shade of blue," she added.

ROCK... AND CHALK

The work is part of a project to reinforce the coast with new sea defences at Cromer and Mundesley.

​As part of the Cromer scheme, contractors are building a rock 'revetment', a sloping structure on the shoreline made of boulders which is designed to absorb the impact of waves and protect the seawall behind it.

The colour of the sea is usually more grey (Image: Mike Page) Rocks have already been brought to the beach by barge from a quarry in the west of Scotland and work is under way to create the revetment, 300m west of the pier, approximately in line with the bottom of the Melbourne Slope.

As part of this, workers have to dig a hole up to 4.5m deep, to create a secure base for the revetment.

It is this work that has changed the sea's colour, by explosing chalk sediment.

Cromer already has reason to be thankful for the chalk layer beneath its beach.

The sea defence project will cost £25 million (Image: Joanna Durndell)
 Just off the coast is the Cromer Shoal Chalk Bed is the world’s longest chalk reef, stretching more than 20 miles along the coast from Weybourne to Happisburgh.

It has provided a living for generations of fishermen, as its rugged bed creates a habitat teeming with crab and lobster.

BAD NEWS... IT WON'T LAST

Those who are enjoying the new waters should make the most of it because council officials say the change will not last.

A spokeswoman for North Norfolk District Council said: "The change in the colour of the sea at Cromer is due to the chalk below the beach.

"The rock is being founded in the chalk layer, which requires excavations as deep as 4.5m for the rock to be placed.

"This is natural sediment, which does not adversely affect water quality, it merely makes the water a lighter colour, particularly notable in the recent sunshine."