More than half of England's coastal communities could see a decline in the number of residents aged under 30 by the year 2039, according to new figures, with seaside towns in northern England set to face the biggest decline.
The figures have been revealed in analysis by BBC News of population projections.
The Parliamentary Group for Coastal Communities said funding cuts meant seaside towns were "being left behind".
The government said it had invested more than £200m in coastal communities.
The coastline in England is home to some of the most beautiful but also poorest places in England.
Some young adults living in Scarborough said they struggled to envisage a future for themselves living by the sea.
"There aren't many career options in Scarborough," said 24-year-old Kayleigh Wilkinson.
"You either work in a care home like I do, or you work in a shop.
"That's one of the many reasons why people my age are already leaving to work in bigger cities like York and Leeds."