In Sanhedrin 108b:3, it says:
אמר רב חסדא ברותחין קלקלו בעבירה וברותחין נידונו
Rav Ḥisda says: With hot semen they sinned, and with hot semen they were punished.
In Torah Ohr 8c-d, the Alter Rebbe says (quoted from Chabad.org here):
Chassidic teachings describe the Flood as a cleansing process. The waters of the Flood are like the waters of a ritual bath—a mikvah—where the waters spiritually cleanse the one who enters it. The world similarly received a spiritual cleansing, setting the course of history on a course of hope and purpose. And just as a mikvah must contain 40 seah (an ancient measure of volume), so did the rains of the Flood last for forty days.
We are commanded regarding the ritual impurity [contained in and emitted by] semen. [I.e., when contracted, one must follow all the laws associated with this impurity.]
Then the question arises: how can these "waters" (possibly שכבת זרע) of the flood be used as a mechanism to purify the world? שכבת זרע is inherently tamei!