"It's really startling when you've been looking at things the size of your fingernail, and you look up to suddenly see something that looks like a 30-foot jellyfish!"

She goes on to explain why we need a parachute for a scuba dive -- and it has nothing to do with the fact that the seafloor will be 5,000 feet beneath us.

This dive is branded by Matye's employer, Jack's Diving Locker, as the "Pelagic Magic" dive (but is simply the "blackwater dive" at other operators).

It takes place in the dark of night about three miles offshore of Kailua Kona, on the "big island" of Hawaii, formed from steep volcanic mountains that drop precipitously into the ocean depths.

Current gyres swirl in the offshore waters, carrying anything in the water in a different direction from the way the wind is pushing a boat on the surface.

The parachute, deployed underwater, anchors the boat into the sea currents, and prevents it from being blown away from the divers.

As an added precaution, all six divers will be tethered to the boat. This is not so much to prevent them from being swept away in the current as to avoid any descents below the 50-foot length of the tether lines.

Most scuba dives are done on a coral reef or other substrate with a hard bottom that prevents divers from going deeper than their physiology will allow.

Not so on this dive.

"Please don't drop your light or camera," pleads Matye. "I'm not going down to 5,000 feet to retrieve it for you."

(CNN)