Berakhot 25B

והכא בטופח על מנת להטפיח, איכא בינייהו.

And here, the difference between them is in a case where it is moist enough to moisten other things. According to the first tanna the prohibition is only in effect when the urine is moist enough to moisten other objects, while according to R' Yosei it applies as long as the urine itself is moist, even if it is not moist enough to moisten other objects.

ירד לטבול, אם יכול לעלות כו׳: לימא תנא סתמא כרבי אליעזר דאמר עד הנץ החמה?

We learned in a Mishnah that one who descended to immerse himself due to a seminal emission must calculate, whether or not he is able to ascend, cover himself with a garment and recite the morning Shema before sunrise. The Talmud asks: Let us say that R' Yehuda HaNasi taught this in the unattributed Mishnah in accordance with the opinion of R' Eliezer, who said: One may recite Shema until sunrise.

אפילו תימא רבי יהושע, ודלמא כותיקין. דאמר רבי יוחנן: ותיקין היו גומרין אותה עם הנץ החמה.

The Talmud immediately rejects this assumption: Even if you say that the Mishnah is in accordance with the opinion of R' Yehoshua, who disagrees with R' Eliezer and holds that one may recite the morning Shema until the 3rd hour of the day, and perhaps the halakha in the Mishnah was directed toward those whose practice was in accordance with the custom of the vatikin, pious individuals who were scrupulous in their performance of mitzvot, with regard to whom R' Yoḥanan said: The vatikin would conclude the recitation of Shema with sunrise.

ואם לאו ⁠— יתכסה במים ויקרא. והרי לבו רואה את הערוה?

We learned in the Mishnah: And if one calculates that he will not be able to ascend and cover himself with a garment in time to recite Shema, he should cover himself in the water and recite Shema there. The Talmud asks: How can one recite Shema with his head above water? His heart sees his nakedness as there is no barrier between them.