Kaya Chotard ties string to a weight on one end and a plastic bottle on the other end. The weight will mark a place on the sea floor while the plastic bottle will float to the surface and act as a marker for an area that will be tested on a subsequent dive.
 Kaya Chotard
Image courtesy of Amy Gusick, Sea of Cortez 2110 Expedition. Download larger version (jpg, 4.2 MB).

Kaya Chotard ties string to a weight on one end and a plastic bottle on the other end. The weight will mark a place on the sea floor while the plastic bottle will float to the surface and act as a marker for an area that will be tested on a subsequent dive.