In Exodus 15:8, this signifies falsities gathered together. Waters normally signify truths, but in this case, where they were blocking the escape of the Children of Israel from slavery and signify the opposite: falsities.

(References: Arcana Coelestia 8286)

To be fruitful relates to goodnesses, and to be multiplied, truths.

(References: Arcana Coelestia 1014, 1018)