A mandatory duty of an Environmental Commission is the preparation of an Environmental Resource Inventory, also known as a Natural Resource Inventory or Index of Natural Resources.

The report is an unbiased objective report on the environmental features and characteristics of a municipality.  It is not a plan in itself but supports municipal planning.  It integrates a variety of data from multiple sources to give the most complete picture possible of natural and cultural resources, critical areas, existing development and infrastructure as well as environmental challenges.It is recommended that an ERI should should be incorporated  as part of the municipal master plan either as an appendix or as part of the conservation element.