have a look at the inshore ACop (L104). the ACoP states: SCOPE AND AREAS COVERED BY THE CODE: 5) This code applies to all diving projects conducted in support of civil engineering or marine related projects and FISH FARMING 14) a person "dives" if he enters water or liquid and in order to survive in such an environment he breathes in air or gas at a pressure greater than atmospheric pressure. From an ACoP point of view and the diving at work regs, it would be difficult to enforce as they are not breathing compressed air. However, From a risk assessment point of view, this is a commercial diving project, and should be carried out using the correct team and equipment. Surface supplied diving or SCUBA if your risk assessment would allow it. Ive yet to come across a diving project yet where the RA and law would allow me to use SCUBA, so snorkels are a bit of a joke really Phil

Have you considered alternative methods to diving? We use a gadget to clean the bottom of our pools which you lower to the bottom and it just trundles around all night and does it's stuff.

Even given the relatively shallow depths, you can still produce a lung over expansion injury, and if they hyper-vent before diving also at risk of shallow water blackout. Its just a massive no no without the correct kit, it would be much more efficient too not having to resurface every 30 seconds. Even in commercial SCUBA we can monitor the divers breathing, and have him tendered on a life line. But unless you have completely benign conditions, with no risk of entanglement or differential pressure, with gin clear visibility, even SCUBA isn't an option. Commercial diving for the unlikely event of being allowed to used SCUBA is a minimum team size of 3. Using surface supplied techniques using tools, 4,5 and above. So if this is just 2 guys in wetsuits, using snorkels, it is wrong on many levels. If you need a hand with the RA, just DM me. Id rather that than read about it in the paper or next ADC safety meeting Phil

Unfortunately I am way from the workplace for a while so won't be able to find out name of kit for a while. I think that they are relatively widely used for pools though. Try searching for "robotic pool cleaners" and see what you think. It might take some maybe not all of the diving requirement away. Good luck.

Just to support what Phil says the regs are quite clear on this and from a medical response...the part I would also include is the response time which will give you the rationale for what systems to put in place short term before reducing the risk permanently with the robotic pool cleaner if that is appropriate...

A simple siphon tube 75mm in diameter is used to suck accummulations from dead spots in the tanks. The problem is positioning the end efficiently which is not easy to see mainly because of the number of fish hence the diving activity. It is something to consider though as we have been talking about using a camera which may be the way forward. The water level is controllable but tends to concentrate the fish and obscure visibility even further but thanks for the comments.