The good news about natural resources law research is that it is basically just administrative law research, which means research in an area of law that is heavily regulated by agencies – immigration, tax, securities, public lands, water, etc.
All this means is that, in addition to statutory, case law, and secondary source research, it is necessary to research the laws and guidance produced by agencies - administrative regulations, agency decisions, and guidance documents.
Why is this good news?
There are a variety of useful immigration law research guides on the Internet that provide an overview of primary and secondary sources used for different areas of research - statutes, cases, secondary sources, regulations, agency decisions, and guidance documents.
Water Law Research Guide Example
You can always find one by Googling something like: water law research guide
I always like the research guides from Georgetown Law Library.