The Sea-Doo was invented by the Canadian firm Bombardier. They chose that name because it resembled the name Ski-Doo, the snowmobile they also invented. Interesting note about the Ski-Doo I found on Wikipedia…

“The Ski-Doo was originally intended to be named the "Ski-Dog" because Bombardier meant it to be a practical vehicle to replace the dogsled for hunters and trappers. By an accident, a painter misinterpreted the name and painted "Ski-Doo" on the first prototype.”