The theme park operator attributes this dramatic loss in profits to a roller coaster crash at one of its theme parks, Alton Towers Resort, in June.
On June 2nd 2015, four people were seriously injured after two carriages collided on "The Smiler" roller coaster at Alton Towers, Staffordshire. Leah Washington, aged 17, had her leg amputated following the crash. The Smiler has since remained closed.
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On top of the ride's closure, Alton Towers Resort remained shut for days following the incident, while other rides across two other theme parks were temporarily shut. Marketing for Merlin's theme parks was reduced significantly too.
"The magnitude of the financial impact is the result of both a significant reduction in revenue and the requirement to maintain an appropriate investment in customer service and marketing through peak season," Merlin Entertainments said in a statement, who added that it was taking action to re-engage with its customers.
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The group expects that this financial hit on the theme parks' profitability may continue in 2016.
The weaker euro had an impact on visiting numbers when it came to Merlin's London attractions, which includes Madame Tussauds and the London Eye.