Just about all of Dry Tortugas National Park lies underwater. If you don't scuba dive or snorkel, this video will show you what lies within the park's Research Natural Area, an area that is closed to fishing and anchoring to help protect marine-life.

This 13-minute video -- which can take a while to load, so be patient -- is the work of the South Florida National Parks Trust, the Environmental Protection Agency and the Florida Keys National Marine Sanctuary. It explains the background that led to creation of the natural area, which is hoped to allow fish populations to rebound and to provide a sanctuary if you will for coral reefs, which face threats from anchor damage, degraded water quality, and warming oceans.

The natural area covers 46 square miles and complements the Tortugas Ecological Reserve, which covers 151 square nautical miles. While the ecological reserve is in deeper water, the natural reserve is more shallow and valuable as a nursery grounds for many fish species. It is hoped that if these nurseries prove to be more productive, the benefits could one day be felt as far away as the Florida Keys.