It has long been said that you mustn’t swim during the Obon holidays. Jellyfish start to appear and the water temperature drops, meaning it’s easy for them to snag your feet and cause paralysis. That’s the general reason, anyway. But there’s another, more spiritual reason why you must not enter the water during Obon.
Obon is when the spirits leave the world of the dead and enter our own. The reason people send lanterns downriver is because they lead spirits back home to the underworld through the sea. That is why during Obon you’ll find many spirits hanging around water.
And it’s not just pleasant spirits who have returned for memorial services during this time. There are lost spirits, lonely spirits, and angry spirits who no longer have anyone to perform services for them. If they happen to run into someone on their way, then they will drag them back into the underworld with them.
You must not swim during Obon. There is no guarantee that you will ever come back out.