Hi - I live locally, surf and work in OSH, so this story about a local surf centre caught my eye.  I'd like to understand how they can manage the risk to an acceptable level. 

I'm interested to hear from any water quality experts and get their take on this, and how hard it'll be to maintain safe water quality.

As I understand it, the algae is safe, but it can make the chlorine less effective which can lead to harmful baceria in the water. In addition to daily checks of PH and free chlorine levels, how frequent would lab testing need to take place for it reassure you the water is safe? I get it might not be a simple answer, but I'd like to get an insight.

Surfers have a higher tolerance to murky water than swimmers, so it might not be a direct comparison, but let's assume swimmers weren't put off by the colour; would a swimming pool stay open with an algae bloom like this? Are there any case studies anyone knows of?

Aware a change in water clarity would have an impact on drowing risk, but I'll assume they have that under control. 

An occupational health & safety platform is not the ideal place to find "water quality" experts.

Typically our general interface is regarding either legionella controls within the workplace or the risks associated with working near/over water from drowning and not any recreational activity exposure.

You would need to refer to the local water authority and the council standards regarding testing/levels/controls. Being very specific to this installation unless you land incredibly lucky (a water board or council employee has access to the actual facility requirememts) your question is likley to have no meaningful response.

Water quality is challenging to manage in the outside environment due to the Sun, which causes a quicker breakdown of chlorine in the water making regulation harder to achieve.  In this context add in the variety of external pollutants and it's easy to see that this would require active management.  

My original background is in swimming pool management, rather than the more natural water environment that you're referring to, where chlorine monitoring is routine and along with external sampling of water to test for other things that can live in water (always interesting).

The Pool Water Technical Advisory Group (PWTAG) would be a great place to start for specific knowlege.