I suggest that you show this rash to your primary care doctor
to make sure it is nothing serious and to determine if it needs to be treated.
There are many causes for rashes like this. As you have already noticed, sometimes the irritation from wet clothing, salt water, or other contacts may cause a rash to start. The dryness and inflammation of the skin that results can take a while to go away, and this can require moisturizers or even steroid creams, especially if you have a history of sensitive skin or eczema
It is also possible that this is contact dermatitis, or a reaction to some chemical or other substance that you have recently come in contact. Common offenders include new soaps or laundry detergents, but there are many possibilities.
A less common cause would be seabather's eruption. This is essentially an allergic reaction to microscope larvae of certain jellyfish, and it is common this time of year, especially in the Carribbean and Florida surf waters (I am not sure where you are located).
If the area becomes more red and inflamed or if you have fever
, these could be signs of a more serious infection and you should seek immediate medical care.