I work for government agency doing environmental enforcement work. Coming into law school, I was pretty set on doing public interest work of some kind.
In the environmental field, I felt like there were relatively fewer entry-level jobs compared to other PI work, such as public defender or legal aid.
I recommend not putting all your eggs in just the environmental basket. Do an internship or two at an environmental agency or nonprofit, do a journal, take classes, maybe do a part-time clinic or an enviro seminar.
But do other types of internships, seminars, and journals and clinics. You are not limited to just your 1L and 2L summers in which to do internships.
I interned during 3 out of 4 semesters in the 2L and 3L year. I did enviro work (journals, seminars, internships, etc.). But I also did a lot of stuff in a different PI field. (Think something like public defender.)
Whatever field you apply to for entry-level jobs, you just want to demonstrate that you are genuinely interested in that field.
I tried to get an enviro job out of LS, but got rejected repeatedly, and I applied across many organizations and states. For example, NRDC, EPA, state departments, regional EPA honors programs, little lesser known nonprofits. No hits.
I worked at the same time and got an entry-level position in a different field. Something like PD. After several years of doing that, I had experience and time (no 3L crunch to get a job) to find the right enviro job for me.
Was it time-consuming to work so many extracurriculars during my 2L and 3L year, on top of regular classes. Yes, it was. I mitigated the difficulty of my classes by taking a lot of clinics and for-credit externships and seminars, though. Not as many bar classes.
Of course, YMMV.