Okay, it is the duck-mobiles used by the Duck Tours. Huge military-surplus, amphibious vehicles with gigantic rubber tires roll around downtown Boston seeing the sites and then go over to the Charles River and plunge in. Meryl reportedly learned to scull for the movie, although a double was used for some footage. Harvard's Weld Boathouse helped with the boats and dock. No one knows.
Many people do.
One fellow, believe me, stands on the dock in Allston fishing on inline skates. A number of people have died trying it. Never try to go on the ice in the Charles. On those seemingly rare days when the snow is adequate, people love to ski everywhere along the lower Charles. As for M.I.T., I am sure they're working on it.