Current Visibility on Koh Tao

How’s the Viz?

Horizontal visibility, or to diver just the ‘viz’, is an estimate of the distance on can see underwater. visibility is important to divers as diving is generally best in ‘good viz’ (better than 10-15m). For research and monitoring, the visibility tells us about important indicators of water quality including sedimentation, nutrient loading, etc.

On the graph below you can find the most current water visibility, ‘viz’, for Koh Tao:



Note: The Horizontal Visibility is assessed regularly by our marine conservation team, using a secchi disk. This is one of the parameters used in our research and monitoring around the island.  One diver holds the secchi disk, while a second diver swims away from the disk along a transect line, the distance at which the disk disappears, and reappears, is recorded. The average of these two values is taken as the viz for that day. Due to thermoclines and other factors the actual viz at different dive sites or depths around the island may vary from these values.

Average Weekly Visibility


The average weekly visibility is a composite of all values recorded from all sites around Koh Tao, based on week number of the year. Week number 1 starts on January 1st and end on January 7th, with a total of 52 weeks in the year.


A day of 'perfect' diving visibility on Koh Tao

A day of ‘perfect’ diving visibility on Koh Tao

Explanation of ‘Viz’ values for SCUBA diving

‘No’ viz: Less than 1 meter

‘Bad’ viz: 1-3 m

‘Poor’ viz: 4-6 m

‘OK’ viz: 6-10 m

‘Good’ viz: 10-15m

‘Great’ viz: 15-20 m

‘Perfect’ viz: greater than 20 m


Percentage of days recorded in 2014 with 10 meter viz or better: 77% (as of Sept. 26th, 2014)