Under Section 12 of the Local Government (Water Pollution) Acts, 1977 & 1990, the Local Authority may serve a notice in writing on any person having custody or control of polluting matter. This notice specifies measures to be taken by the person in order to prevent or control the pollution of the water concerned.
It is an offence under Section 3 of the Local Government (Water Pollution) Acts, 1977 and 1990 to cause or permit any polluting matter to enter waters. A person who permits polluting matter to enter waters shall be guilty of an offence and shall be liable to prosecution by the Local Authority, the Fisheries Board or any other person. Pollution may originate from a number of sources including agriculture, forestry, industry or badly constructed or badly maintained septic tanks.
Section 12 Notices
Under Section 12 of the Local Government (Water Pollution) Acts, 1977 & 1990, the Local Authority may serve a notice in writing on any person having custody or control of polluting matter. This notice specifies measures to be taken by the person in order to prevent or control the pollution of the water concerned.
Furthermore a person who does not comply with the terms of a Section 12 Notice shall be guilty of an offence and shall be liable to prosecution by the Local Authority.
https://www.irishstatutebook.ie/eli/1977/act/1/section/12/enacted/en/html

Note: potentially used as a tool to get controversial pollution matters solved quickly as the order relinquishes the entity being enforced upon from applying for planning permission. This could be used specifically to keep certain enforcement matters under the radar as planning permission triggers a public process etc
Local authorities do not appear to publish Section 12s. FOI/AIE is only channel to request disclosure
Examples:
https://irishriverproject.com/category/section-12-water-pollution-notices/