| Abbreviation | Definition |
|---|---|
| MTFR | Maximum Technically Feasible emission Reductions |
| MTR | Maximaal Toelaatbaar Risiconiveau (Dutch: Maximum Admissible Risk) |
| MTRCA | Metropolitan Toronto and Region Conservation Authority former name of the TRCA prior to Toronto amalgamation |
| MTRCA | Metropolitan Toronto and Region Conservation Authority — former name of the TRCA prior to Toronto amalgamation |
| MUFW | MUtant fish in Fresh Water |
| MUSYA | Multiple Use-Sustained Yield Act |
| MVC | Mississippi Valley Conservation [Ontario, Canada] |
| MVCA | Maitland Valley Conservation Authority [Ontario, Canada] |
| MVPZ | Minimum Vegetation Protection Zone |
| MWDT | Mixed Waste Disposal Trench |
| MWH | Maine Watershed Habitat |
| MWHA | Maine Watershed Habitat Analysis |
| MWLAP | Ministry of Water, Land and Air Protection |
| MWLE | Ministry of Water, Lands and Environment |
| MWMS | Municipal Waste Management Strategy |
| N | Noise |
| N | Noxious |
| N | Nature |
| NAAEC | North American Agreement on Environmental Cooperation |
| NABCI | North American Bird Conservation Initiative |