Key West Tours http://goarticles.com/article/Miami-to-Key-West-Tours-for-Discounted-Prices/6664014/
You will be on an amphibious vehicle that is able to go through the water and sea. However, the downfall here would be the fact that it only lasts from Washington Ave to Collins Ave, then goes into the water and circles around Fisher Island, so it's a fairly short tour.
Brochure information http://www.articledashboard.com/Article/How-does-digital-color-brochure-printing-work/2950785