The Turquoise Trench is a location in the game. It's essentially a big ol' fissure in the bottom of the ocean. It is very dark and deep.
Did you know that the main story quest sends you down into the Turquoise Trench? Because it does.
Did you know that the daily Kojin quests ALSO occasionally send you into the Turquoise Trench? Because they do.
Did you know that one of my greatest fears is being in dark or murky water? Because it is. Oh my, it is.
I know that there's nothing swimming around in there, but it still freaks me the heck out the way things appear out of nowhere and it takes so long to get to the bottom and WHY DO YOU KEEP SENDING ME THERE, KOJIN?!
Wait, WHAT?! There's a fishing spot down there, too?!
. . .
*sobs*
Be strong little one, for your strength as warrior of light knows no bounds. Be it 100 foot tall monsters, or 1000 feet deep dark murky trenches you shall persevere.
I dunno, man. I'm not sure how many mild heart attacks a person is allowed to survive, Echo-blessing or no.