Immersing in a natural body of water often raises the following halachic considerations:
Modesty
A woman may immerse wearing a loose-fitting long shirt or robe that allows the water to reach all parts of her body. Alternatively, if there is sufficient privacy, she may enter the water with a robe or other easily removable garment and remove it under water.
Timing
In pressing circumstances, as when a location is unsafe at night, a question should be asked about the timing of immersion. A woman in this situation may be permitted to immerse on her scheduled mikveh night after sunset before nightfall. Alternatively, immersion may be permitted during the daytime following mikveh night.
Following immersion during the daytime, the couple may not have relations prior to nightfall. In this scenario it is preferable for the couple not to see each other between immersion and nightfall. If this is not feasible, they should avoid being secluded alone together.
Supervision
Mikveh immersion should be supervised in order to ensure that all hair is submerged. The site needs to be sufficiently well-lit for the person watching to be able to see this.
With a natural body of water, supervision can also be essential for safety.
Any halachically observant Jewish woman over the age of twelve can supervise immersion. If no woman who meets this description is available, a woman can immerse without supervision if a she has short hair or can otherwise ensure that her hair is thoroughly submerged, as with a loose hair net (cutting the elastic so that it is not tight against the head).
Alternatively, a woman’s husband can observe the immersion. Since it is not permissible for him to see her unclothed while she is niddah (even moments before immersion), she should be especially careful with modesty (as above).
