At Corkscrew Swamp Sanctuary, burn boss Mike Knight uses fire to preserve ancient habitats in the area, including the last remaining stands of old growth bald cypress. Before his entire team arrives, Mike scouts the location of where the fire will be started. He is joined by Evan, an intern who has a passion for restoring nature. Mike shows Evan around the site. He explains how these environments need fire to thrive and also warns him of some of the dangers of setting off a controlled burn. The rest of the crew arrives and they start lighting up sections of the sanctuary. Mike explains that, as much as they try to control the direction of the burn, nature ultimately decides. Sections of the fire start getting out of hand, and some of their equipment fails. However, the crew takes every precaution, making sure the operation runs smoothly. In the end, the burn is successful and Mike and Evan reflect on how important these processes are to preserving old ecosystems. On the Florida panhandle, underwater cave divers Brett and Matt swim over 2400 feet into the dark abyss to search for signs of a potential sinkhole that is degrading the precious Floridan aquifer. Brett and Matt are extremely experienced cave divers. Cave divers have discovered trash in a remote section of the cave, so today they are bringing a device called a radio locator to see if the trash is coming in through an aboveground sinkhole. They also bring Becky, who will be filming their journey. As they get ready to enter the cave they make sure all of their equipment and backup air tanks are working. Brett explains that they must take a redundant amount of equipment, since there is only one way in and out of the cave, and they don't want to get trapped. The divers scooter through the cave until they finally find the room with the trash. They battle the heavy flow as they attempt to place the radio locator in the proper position so that the team above the surface can follow its signal. By the time they get the locator in place, Brett is running out of gas in his air tank. He is able to replace his tank with an extra one as they successfully swim out of the cave. The signal from the radio locator leads the aboveground team directly to a sinkhole, confirming how the trash made its way to the bottom of the cave. In the end, Brett explains how precious and fragile the Floridan aquifer is and how we must continue to protect it. Off the coast of Tampa, maritime archaeologist Nicole Morris dives to an old Civil War shipwreck with Danny, a descendant of one of the sailors who died in the shipwreck. Danny has done intensive research on his family tree and found that he is the descendant of a crewman on the USS Narcissus, an old Civil War tugboat that sunk near Egmont Key. Nicole and Danny ride to the wreck's location as Nicole explains to Danny what parts of the ship they will be seeing. Danny is very excited when they arrive at the site and dive in, even though the visibility underwater is not perfect. Nicole lets Danny touch the boiler, a part of the ship his ancestor would have used, and then she takes him to the plaque that recognizes this wreck as a state archaeological preserve. Danny is very moved and thanks Nicole for taking him to witness this personal piece of history.