The voluptious sunbathing Jalakanyaka (mermaid) at Shankumugham Beach in Thiruvananthapuram was created using concrete, and is about 26m (87’) long. map
It was created by award-winning sculptor Kanayi Kunhiraman on the beach in Thiruvananthapuram, close to the airport, in a park with other large sculptures.
It is by far the largest mermaid statue I have encountered so far, and is probably Earth's largest mermaid sculpture.
References:
● https://commons.wikimedia.org/wiki/Category:Sagarakanyaka_(Mermaid)
● https://www.keralatourism.org/photo-gallery/jalakanyaka-shanghumukham-beach/6
● https://youtu.be/swwEfmIGkn8
● https://www.hindustantimes.com/india-news/kerala-art-lovers-fume
● The Mermaids of Earth coffee-table book: See page 175 in the book about this sculpture.