Snorks
According to the Snork back-story, a few ventured to the surface (which the Snorks believe is "outer space") in 1643, and watched a Royal Navy ship being attacked by pirates. The captain wound up in the water, and that was the first contact between the species when the Snorks saved his life, to which the captain then expressed his gratitude by writing a book about the Snorks, although very few humans believe in the existence of the Snorks. Since then, Snorks have adopted several human habits, such as wearing clothes.