Large animal in river sinks carrying naked person over (12)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

HIP (trendy; in) + PO (river in Italy) + ( POTS [sinks, as in a snooker player POTS a ball in a pocket to score points] containing [carrying] h UMA n [person] excluding the outer letters  H and N [naked] and then reversed [over])