My brother has a pond at his work that he tried this and it worked pretty well. I will get him to post about his experience. That being said there isn't much about the dye itself that needs to be taken into consideration. Just make sure that it is highly visible. We use a pond dye for well dying ponds. This is what I told by brother to use.
One thing to consider though is unless your leak is flowing rapidly it may be hard to determine exact sight of leakage. If possible look behind, If on a dam look on backside for wet spots. That will help narrow down your search area.
