Alton Towers saw a "25% drop in visitors" in 2015, which is a bigger decline than any other large theme park in Europe, according to a report.
Themed Entertainment Association (TEA), which reports theme park attendance at global attractions, said this was down to the Smiler ride crash in June 2015.
Five people were severely injured in the crash at the Staffordshire park.
Owners Merlin Entertainments said TEA's figures were estimates and not confirmed.
Thorpe Park in Chertsey, which is also owned by Merlin, was the only other theme park in Europe to see a decline in visitor attendance, according to the Global Attraction Attendance Report (GAAR).
Merlin's Resort Theme Parks Operating Group released figures in February showing "revenue declined by 12.4% due to the significant fall in visitation at Alton Towers following the accident on 2 June".
However, the company does not provide a breakdown of visitor attendance at their individual theme parks.
American firm AECOM compiled the figures in the GAAR and state in the report where they "do not receive specific park level figures from the operator" they use a "detailed methodology" considering factors such as new rides, ticket prices, media coverage, amongst others.