I had a flick through Goggle and came up with this...
Ponds
Exemptions from approval for fish ponds, water storage ponds, ponds for water features and fountain ponds
Exemptions from development and building approval may apply to certain ponds not inside a building provided they comply with relevant provisions of Regulations. Examples of ponds not inside buildings include fish ponds, water storage ponds, ponds for water features and fountain ponds.
Exemptions from development approval
The development does not need development approval if it complies with relevant provisions of the Planning and Development Regulation 2008, Schedule 1. The following is a summary of the provisions and is correct as of the date the web page was last updated - scroll to the bottom of the web page to find this - however the Regulation's Schedule may have been updated since then. In summary, the development is exempt provided that:
:it is not for, or not used for swimming, wading or bathing;
:the maximum water depth is not more than 300mm;
:the surface area of water is not more than 6m2 when full (without overtopping effects);
:no part is between a front boundary and a building line for the block;
:no part is within 1.5m of a side boundary or rear boundary for the block;
it complies with relevant general exemption criteria.
See definitions to understand the terms in italics.
Exemptions from building approval
The development does not need building approval if it complies with relevant provisions of the Building (General) Regulation 2008, Schedule 1. The following is a summary of the provisions and is correct as of the date the web page was last updated - scroll to the bottom of the web page to find this - however the Regulation's Schedule may been updated since then. In summary, the development is exempt provided that:
:it is not for, or not used for, swimming, wading or bathing;
:the maximum water depth is not more than 1.2m;
:it will not affect the structural integrity of any part of a building for which a Certificate of Occupancy or other certificate under the Building Act 2004, part 5, has been issued;
:it will not affect a fire-rated wall, ceiling or floor;
:it will not affect a ventilation or air-handling system, fire protection system or other mechanical service;
:it will not affect a fire escape, emergency lift, stairway, exit or passageway to an exit;
:it will not affect the natural light of ventilation available to a building for which a certificate under the Act, part 5, has been issued;
:it will not affect the building in a way that reduces its compliance with the Building Code to a level that is less than the minimum requirements of the Code;
:it does not involve handling asbestos or disturbing friable asbestos (other than minor maintenance work, i.e. low-speed or hand-drilling, sealing, painting, coating if done personally by the owner or occupier of the premises)..
No building approval, licence, notice, certifier, plans, inspections, certificates, design or construction standards required under the Building Act 2004.
Hope that helps. | 
