The choke factor is visible in tournament-style athletics competitions, and should teach managers about incentives.
The possible culprits are: a sudden algae bloom; a change in pool alkalinity; or a chemical reaction in the water. How do these cause a change in the colour of the water?
Africa has a number of excellent scuba diving sites, but these must be maintained sustainably to keep attracting different divers.
Diving in many parts of Indonesia, Thailand and Malaysia now costs a little more than it used to – but you might be happy to discover why.