Visibility

The horizontal distance a diver can see underwater, ranging from under 1 m in silty lakes to over 40 m at clear tropical and volcanic sites.

Visibility, or viz, is the horizontal distance at which a diver can distinguish objects underwater. It ranges from arm's length in a stirred-up quarry to 40 m and beyond at sites like the volcanic islands of the Azores, the walls of the Red Sea, or the freshwater cenotes of Mexico. Divers usually estimate it in meters or feet and report it in the briefing and the logbook.

Viz is controlled by suspended particles: plankton blooms, river runoff, stirred sediment, and surge all reduce it, while deep clear ocean water and filtered spring water maximize it. It often changes with depth, improving below a murky surface layer or collapsing near a silty bottom. Low viz shrinks your effective buddy distance, makes navigation harder, and raises the value of a dive light and compass even in daytime.

Estimating viz honestly is a skill: a common method is judging when your buddy or the reef fades to a silhouette. Recording viz for every dive builds a personal map of how each site behaves by season, which is one of the most useful patterns a dive log can reveal. Remember that vertical visibility often differs from horizontal, so judge both before committing to a plan.