The Round Trip the Wind Ruins

A ferry crosses a lake from its home dock to an island and back, cruising at the same speed through the water the whole way. One afternoon a steady current runs directly from the dock toward the island: it raises the ferry's ground speed on the way out by exactly the amount it lowers it on the way back. Compared with a day of perfectly still water, is the round trip faster, slower, or the same — and why?