There are a number of requirements for the use of a natural spring as a mikveh. First of all, the spring itself has to meet the requirements for immersion. The water must originate from the spring and not from a collection of rainwater, and it must be deep enough so that you can immerse your entire body at one time. The spring you describe, which reaches your neck, is certainly deep enough.

You must be certain that the area in which you immerse is safe. Moreover, it should be private and clean enough that you will not rush your immersion.

There is also the issue of modesty that you raise. A loose-fitting dress (or shirt or robe) could, as you suggest, address that concern and would not impede the kashrut of the immersion as long as the water touches all parts of your body.

In addition, someone should witness the immersion to check that all all your hair is under the water. (This requires sufficient lighting.) Any halachically observant Jewish woman over the age of twelve can supervise immersion. If there is no woman who meets this description available, then you could immerse with a loose hair net (cutting the elastic so that it is not tight against the head) to ensure that your hair is submerged. Alternatively, your husband could witness the immersion (in addition to acting as look-out). Since you are still niddah prior to immersion, he should not see you unclothed. Thus, even if there are no other swimmers that night, you should wear a loose dress, robe, or long shirt into the water.

Please see our article here for further discussion of immersion in natural bodies of water, and feel free to get back to us with any further questions.

This response was updated on 12 May, 2024.