Here are some ways that citizen science observations like those on iNat can factor into an EIA/EIR (based on experience from California, but possibly generalizable elsewhere).
The developer of a typical large development project will need to provide some type of assessment that shows what impacts might be caused by the proposed project and by various alternatives (one being the “no project” alternative). There are broadly similar requirements under the California Environmental Quality Act (CEQA) and the U.S. National Environmental Policy Act (NEPA). I’m guessing Canada has something similar.
Usually the developer will hire a lead consultant firm to prepare the report and they will hire specialists in various areas including “biological resources”. The biologist will research the site and possible species of concern, and try to determine whether they are (ever) present on the site, and in some cases whether the site represents potential habitat (e.g. for an endangered species that’s subject to a restoration program). There will then be field survey work (ideally at several times of year) to establish the presence of possible species at the site.
From what I have seen, there can be more focus on demonstrating the absence of improbable species with higher levels of protection (e.g. federally endangered fish, even at urban sites with no obvious surface water) than there is on determining the presence of moderately rare but less improbable ones (e.g. locally rare plants).
So how might iNat observations help? Maybe the consulting biologist will check iNat (or GBIF) when they do their research and see that a species of concern has been reported at the site, or in the immediate area. That should help ensure they then try to validate the species’ presence during the field survey. Of course that can be difficult with mobile and seasonal species.
But it’s not all dependent on the professionalism of the hired biologist. Even if the EIA/EIR ignores iNat data, it’s still possible for a local or national nature protection org (or the state’s own environmental protection employees) to use that same iNat data to provide input during the decision process. This could be as simple as submitting a comment that says “The EIR says there’s no evidence of Ivory-billed woodpeckers at the site and that none were found during the field survey, but the data from iNaturalist shows the species has been recorded from the site three times in the past five years. The EIR should be revised to address the likely impact on the only remaining population of this species.”
The CEQA process requires the revised EIR to then address any substantial criticisms. And even if the developer’s consultant chooses to cast doubt on the iNat data, decision makers can decide whether they’re willing to certify the EIR over objections to its adequacy. In important cases, these decisions may be appealed in the courts, but the foundation of any case is the EIR and any comments by the public and government bodies.
iNat data can also feed into this type of process more indirectly, by informing the designation of protected species in the first place. Before the boom in citizen science, information about the distribution of less common organisms could be quite sparse (even if it was potentially of higher quality because it might be gathered by trained professionals, backed by herbarium/museum specimens, etc.) Now that there are more observations from sources such as iNat, biologists working on protection assessments for specific taxa can get a better picture of current distribution.
It could be that an iNat user documents an undiscovered or lost population of an unusual species, leading to it receiving protection from the state. Alternatively, iNat observations might show there are many previously unknown populations of a supposedly rare species, justifying moving that species to a lower tier of protection. Of course, all of this would ideally be backed up by field research by professionals, but the original information source would be iNat users.
Lastly, it seems that including citizen science as part of EIRs has now become California policy. As an example, the City of Sausalito recently issued a draft EIR for its proposed 2040 General Plan update (under CEQA, major government initiatives can require an EIR, not just specific developments). In response, the California Department of Fish and Wildlife (CDFW) asked the city to update its proposed criteria for biological assessments to add the following language (my emphasis):
The special study shall be conducted by a qualified biologist and shall minimally include a data review and habitat assessment, prior to Project approval, to identify whether any special-status plant or animal species’ habitat or sensitive natural communities occur on-site. The data reviewed shall include the biological resources setting of the EIR and the best available current data for the area, including an updated review of the California Natural Diversity Database (CNDDB) and relevant citizen scientist data such as iNaturalist. Habitat assessments shall be completed at an appropriate time of year for identifying potential habitat and no more than one year prior to Project activity commencement.
So if you submit an iNat observation of something rare near a development site in Sausalito (or presumably any other part of California, in time) then the developer will be required to take account of it!