Police had to break up a gathering of more than 3,000 people on Bournemouth beach because the organisers failed to secure a licence.
The Sierra Leone Brighton Association advertised the "Sierra Leone Day" but no-one told the authorities.
The advertisement said a sound system would be "blasting out the latest tunes throughout the day".
It is thought people travelled from across Sussex and London to attend the party, which was dispersed on Saturday.
The association provides a support network for Sierra Leone immigrants and refugees living in Sussex.