פירוש על בבא מציעא 42:3

By the tide (zuto) of the sea - Places on the seashore, where it is the way of the sea to return [to the shore] ten or fifteen parsa twice a day, so it sweeps away that which it finds there and goes. Zuto is an expression of largeness and expansion in the Greek language; like the sages wrote [in their Greek translation] to King Ptolemy, "and upon the exalted ones" (Exodus 24:11), [as] "and upon the zatuti" (Megillah 9a).

Or by the flooding (sheluliyato) of a river - when it expanded and overflows its banks and takes booty (sholel shelal) and sweeps away that which is found.

The Merciful One permits it - and even when it comes to the finder before abandonment [by its original owner].

Below - in our discussion, "From where do we know that a lost object swept away by a river, etc."