You can buy underwater / splash bags for cameras that are basically very thick zip-lock bags. They're much cheaper and lighter than a true (rigid) underwater photography enclosure, but they're basically airtight above water and will keep the dust off your gear. You won't be able to change lenses, however, and zooming might be difficult or impossible, so you'd probably be limited to just putting on a 24mm lens and shooting that all the time.

http://www.bhphotovideo.com/c/product/547694-REG/DiCAPac_WPS...