Hmmm… must be swamp gas … metallic, disc-shaped swamp gas … right …

http://news.co.cr/best-ufo-photo-in-the-world-taken-at-arenal-costa-rica-45-yrs-ago/50584/

Actually, this provides an excuse to discuss the phenomenon of USOs, or unidentified submerged objects …

And, did I mention, this is a subject touched upon in Flying Saucers!