Can a river be used as a woman’s Mikvah?
There are several issues with using a river for a Mikvah:
1. The river must not stem from rainwater, unless it’s stagnant – not flowing. Pipes through which water passes can also invalidate the water. Even if the river originated from a spring, if often increases due to rain water or melted snow.
2. Also, the water must be stomach-height so the entire body could be immersed at once; at the same time, it may not be too deep that people would be afraid to immerse there.
3. Additionally, it must be a safe place to Tovel. Aside for safety per se, the fact that one is concerned for their safety while Toveling can cause them to Tovel quickly without focus on doing it properly.
4. The area must be well lit that whoever watches you Tovel will be able to ensure that your hair is completely submerged under the water.
5. The floor of the river or shore often has mud or other substances that can stick to your feet.
6. One should not Tovel in a time or place where they are concerned that others might see them when immersing.
Due to all of these reasons one should not Tovel in a river unless no other choice exists. Even then, one must consult a Rov as to the Kashrus of the river for Tevila.
.שו״ע יו״ד רא, ב. רמ״א שם. דרכ״ת שם כ-כא. שו״ת חת״ס יו״ד רב. שבה״ל ד, קח. אג״מ יו״ד א, קפה
.שו״ע יו״ד קצח, לד. דרכ״ת שם קיח. שו״ת שרידי אש ב, מד
.שו״ע שם לג. רמ״א שם. פת״ש כ