For some reason politicians who don't normally love public transit have a soft spot for ferries. The capital startup costs can be pretty low - a boat, maybe a couple of docks - but the subsidy per ride is generally obscenely high, and ferries usually don't go from population center to employment center. They're generally low ridership boutique travel options because they don't quite go from somewhere convenient to somewhere convenient. (Yes, of course there are exceptions). They aren't very fast.
Probably would get a bigger bang for the buck by subsidizing bike sharing more.