Different municipalities across the country have different rules and regulations covering ponds. It is always recommended you check with your local councils planning department if you are thinkning of putting in a pond.
You may require a building permit for your pond, but the requirement for a building permit differs across municipalities. Whenever undertaking a building project of any size it is a good idea to check with your local councils planning department for any restrictions you may have and whether or not you require a permit. It is better to do the work now rather than having to remove your pond in the future.
When talking to your council, it is also a good opportunity to discover the location of power, water and waste services on your property. Some of these services are exceptionally easy to damage and quite costly to have repaired. In the case of 240 volt electricity, they can also be deadly. Knowing the location of all your services beforehand is very important prior to commencing any excavation.
One common misconception is that ponds over 300mm deep require pool fencing, and this is definitely not the case. Some people may wish to install fencing or a subsurface mesh for safety or protection, but they are not required. The Building Comission has released a guidelines booklet directly addressing this problem, which can be found here on their website.