Mermen and merchildren welcome too
Plymouth hopes to end the day with a world record to its name.
Mermaids and mermen - collectively known as merfolk - will be at the newly glittering Tinside Lido, hopefully in sufficient numbers to bust the current record.
Merchildren are taking part too.
More than 550 merfolk have already registered to take part in the event at the pool on Plymouth Hoe from 9.30 a.m. on Thursday.
Plymouth is home to the UK’s first National Marine Park
Merfolk have to turn up as half human, half fish merfolk to be part of the record attempt in the art deco Grade II listed salt water swimming pool.
The event has been organised by Pauline Barker, founder of Devon and Cornwall Wild Swimming with the support of Plymouth Active Leisure, the National Marine Park Horizons Project and Plymouth City Council.
The Plymouth Sound National Marine Park is said to be a natural habitat of merfolk.