Disney dyes all the time.
The waterways of Disney are almost always green where guests need to imagine what might be beneath. For instance, some rides roll on tracks through water but feign to be boats. If guests could see the tracks it would spoil the illusion. Also, the water hides many secrets, dropped trash, cameras, and even stuff like wheelchairs. No kidding. When they drain the green water to clean the attractions, they find everything under the sun… er, water.