As well as a boat this image by the Curiosity Mars Rover, Sol 995 May 25, 2015 has a mysterious leaning tower upper right center!

There are boats in this Spirit Rover frame taken in 2009.

This craft photographed by the Curiosity Rover on Sol 782 Oct. 18, 2014, looks like a cable ferry.

Looks like a couple more water craft on Curiosity Sol 1255.

Another one at Curiosity Sol 51.

Martian Boat @ "Rocknest."