In our field scholarships are often a lump sum of financial aid. These are most commonly available to undergraduate students, and usually do not entail much beyond the cash they provide. They can be based on merit, need, or both. Fellowships are different from scholarships in that they don't necessarily include financial aid, though they usually do. Fellowships are typically targeted towards graduate students and post-doctoral researchers. If you receive a fellowship award you become a "fellow" which typically entails a relatively high degree of interaction with the organization that granted the fellowship. This could include attending trainings and providing them with periodic reports and content for newsletters and things like that. Fellowships are more commonly merit-based and are commonly associated with a specific study system and/or organization. Any proposed research will have to be applicable. Though universities also offer internal fellowships for graduate students that are not necessarily tied to any course of research.
The NSF provides many fellowship opportunities. You can learn more here and search their different grants and fellowships via the links below. The UC system also has info and resources.
Other Fellowship Opportunities
https://seagrant.noaa.gov/graduate-fellowships
https://manoa.hawaii.edu/graduate/fellowships-scholarships/
https://www.unr.edu/cse/graduate-program/fellowships
https://grad.ucla.edu/funding/#/
https://deltacouncil.ca.gov/delta-science-program/research-funding-and-fellowships
https://wfscjobs.tamu.edu/?job_category=fellowships-scholarships
https://www.mammalsociety.org/grants