there's something in the water.
you see it, sometimes; a great liquid thing, languid and loose like oil. it pulses in slow bursts of light and leaves behind trails of lighter, cleaner ocean in its wake. you think it might be cleaning it. does it eat? you've never seen it eat. it seems to prefer simply... floating, bobbing along with the currents, occasionally propelling its body forward to glance at sea life.
you wave at it. it waves lifts its large head and trills.