In some states, a fishing license may be all that is needed. In others you will need a scientific collecting permit. Of course, the collection of state or federally endangered species carries severe penalties. These regulations are necessary to protect an already overharvested group of animals. Just as important as securing the permission of the state is securing the permission of the landowner.
Riparian rights are complicated and differ from state to state.
When possible, try to get permission. Lastly, if you do collect, it is best to take only dead shells until you are familiar with identification. You do not want to find that you have killed an endangered species by mistake. We started this essay with the finding in 1987 of the extremely rare Epioblasma obliquata perobliqua in a small Ohio creek. To our knowledge, it does not occur anywhere else on earth.