It's in the Tail
Water does not hinder the hairstyle of the mermaid as most times it is braided or allowed to lay freely to glide through the water. She may choose to place shells, flowers, sea plants, and comb accessories in her hair.
A true mermaid is naked, but the laws in many countries ask that the female not bare her chest. There are beautiful fabrics for making the bra or a swimsuit bra may be purchased. Most often the fabric which is used in the tail is also used for the bra.
Fabric stores stock special two-way stretch fabric designed for making sea creatures. These fabrics do have scales imprinted in their design to offer fish-like lookalikes. Young girls are delighted wearing a tail made from these fabrics. The tail is very easy to make. The fin is challenging.
The fin will require your creativity and ingenuity to have it able to flip and flop through the water as well as to give the swimmer speed as it cuts through the water. There are many online diy ideas and instructions for making these fins using rubber mats found in the home. Or, if preferred specialty stores do carry the supplies for making fins.
Not a diy person? Mermaid supplies are available at specialty stores. The serious-minded mermaid student and professional entertainer will want to purchase a professionally made costume. These are the costumes which are modeled or used in the movie industry or worn by mermaids performing at tourist locations.
Need more information? Read An Introduction to Mermaids