Each region has local laws and regulations governing diving practices, as well as unofficial "best practices" used by the local diving community. Compared to other regions, Zurich is surprisingy relaxed in this respect. 

Dive flag laws. Each party of divers requires a standard blue and white dive flag. This should be displayed prominently by your entry point. Failure to comply could result of fines of CHF 200 per diver, and is strictly enforced. The flag informs boat traffic and windsurfers that they must stay at least 50 meters away from the flag. Whether this is known to these groups, or whether the rules are as strictly enforced on them as they are on the divers, is a matter of debate. One thing is clear however - not having a dive flag can be expensive, you can obtain a suitable flag from most dive stores in the area, they usually cost around CHF 50. The flag laws are valid not just for Zurich, but the whole of Switzerland.

License requirements: Switzerland does not require a separate license to dive in Swiss waters. A valid open water certification from a well known diving organisation (e.g. PADI, CMAS, SSI etc) is all that is required to obtain fills, rent equipment etc. At the professional level no restrictions exist concerning instructors or divemasters and their freedom to teach in Swiss waters.

Dive site restrictions: Generally no restrictions exist at most sites, and since almost all lakes in Switzerland are publicly owned, no written permission or entrance fees are required to dive. Exceptions may exist for some sites with previous accident histories, the police may request that you register with them to dive first, or require additional qualifications, but such exceptions are rare. If in doubt, seek local knowledge

Solo diving: Diving without a partner is not forbidden by law, but strongly discouraged unless you have specific training, experience and equipment for this style of diving.

Regulators: It is common practice for divers in Swiss waters to use dual first stage regulators. If you experience a free flowing second stage, it is a simple matter for your buddy to shut down the associated first stage, avoiding the loss of your breathing gas. Of course it is possible to dive using a single first stage, but if you plan to go into deeper, colder waters, consider buying an additional first stage.

Other equipment: Smaller lamps used in tropical locations may not be considered sufficient for the conditions here. Thinner gloves or wetsuits used in warmer waters may not offer you the level of thermal protection appropriate for our waters. Seek local knowledge or the advice of a dive store if in doubt.