Odds of Getting In
Employment opportunities for biological scientists (that's you, the limnologist) are expected to rise faster than most other jobs. Anyone environmentally-educated and motivated will be able to break into their chosen vocation: ecologists, botanists, and general biologists.
When you really think about it, water is our most precious resource and most of us Westerners take it for granted. The limnologists, botanists, and aquatic scientists are the ones who are going to figure out how to ensure we all have enough water for a long time. We hope.
If you decide to go the doctorate route and try to get a job—or even a grant—via academia or research, you may find yourself among stiff competition. So plan your course of direction carefully.