Similar to all these "mythical monsters" which Jeremy Wade investigates in "river monsters". By the end there is always an explanation, with no sign of a true monster.
People's recollections of a sighting or something they've heard are passed on like chinese whispers over the years and before you know it we're at the Abominable Snowman, Bigfoot, Loch Ness Monster and Father Christmas stage, lol.
I've seen countless documentaries on our Loch Ness Monster. Decades ago people never knew what was lurking in the depths but the technology has improved so much over the years they've virtually scanned every square inch of Loch Ness, several times. Nothing has ever been found. However, people genuinely love the mystery of this type of stuff, not to mention the money generated.
Personally, to answer the question, no I don't believe in any of it but in the same breath I say good for the people who do believe in it all.
PS. I do, however, believe in aliens. The universe is too vast for us to be alone, and the distances too immense for any interstellar civilisations to ever meet anyway. Even travelling at the speed of light will get you nowhere in the scale of the universe.