Many Chassidic men are accustomed to go to mikvah on Shabbat morning. Keeping up this practice on vacation may present some challenges:

1) Immersing oneself on Shabbos in a sea or river raises several issues. Most significantly: the issue of carrying. The sea or river will normally be defined as a “karmelit,” wherein we may not carry anything beyond four cubits. After immersing, one's body is covered in water. At first glance, it would appear that he may not walk more than four cubits within the sea. There are, however, some authorities who do permit walking within the water, on the pretext that the water on the body is still attached to the sea.1

Clearly, though, one is forbidden to walk out of the water whilst his body is covered in water, for, in effect, he is “carrying” the water. If that coast has the status of reshut harabim (public domain), then the violation would be “carrying” from akarmelit to a reshut harabim. If the coast is defined as a karmelit, then the said issue of “carrying” the water on his body applies to going beyond the immediate four cubits.

2) Dipping while wearing a bathing suit: I was always under the impression that this was not allowed. But I recently saw2 that some poskim do allow this, and even permit getting dressed and returning home through the public domain while wearing the wet garment!

Note: the discussion here is about immersing, not about swimming. As is common knowledge, swimming is not permitted on Shabbat.

3) A regular swimming pool is not valid as a mikvah (primarily due to the filter being in operation). Yet for the purpose of men’s immersion in the morning, some poskim do see value in immersing in a swimming pool.3

4) Conversely, tevilah in a tub of water is of no value, since the water is in a keli (a portable container). Some people have found a solution: They acquire a portable pool, but then cut a hole in the floor of the plastic liner, so it's no longer a keli. Once the pool is in place, cement is poured over the area of the hole. This blocks the hole whilst simultaneously connecting the tub to the ground beneath, thus making it into a mikvah that is valid min haTorah. Miderabanan that mikvah is not valid, because its water was not filled naturally. It’s therefore not acceptable for immersing vessels, but for the men to tovel in the morning it may suffice.