All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
If you mean that urinating in this water could have rendered this water impure and your body became impure by you touching this water with all your body and you think that you are obliged to perform Ghusl (ritual bath) in order to become pure, then the answer is as follows:
If this is what you meant, then you should know that it is not possible for sea water to become impure as it is a huge quantity of water, as regards the swimming pool, then if its water is a huge quantity to an extent that urine does not change its colour, taste or smell, then this is like sea water, but if this swimming pool is of a small quantity of water to an extent that urine changes it [its colour, taste or smell] then all the body becomes impure because of this; and you are obliged to wash your body with pure water.
However, if you meant by Ghusl, cleansing with water when one urinates when swimming in the sea, then there is no harm in this, and you are not obliged to cleanse as when the water passes over your private parts, it cleanses them. The same thing applies if the water of the swimming pool is a huge quantity to an extent that urine does not change it. However, if the water is a small quantity and urine changes it, then all your body becomes impure and you are obliged to wash all your body and not only your private parts.
Allaah Knows best.