Ok, now here is what happened to me;
I lost a disc over a fence and it landed between the fence and a bayou in some very think, waist tall grass. We had to walk two blocks just to get around the fence , and myself and two friends searched for the disc for quite a while. I found a JLS and a DX Aviar, but I didn't find my custom dyed Star Coyote. I was very bummed out, and I thought it was gone forever. Two weeks later, I got a call from a guy that found my disc. He said it looked like a special disc , and it must be missed. I met the guy, and offered him money, or a disc from my bag, but he didn't want either one. I was very happy to get my disc back.
Now, that being said, you can't say that someone threw their disc away in the water, or tall grass, and walked away. My disc was search for by three people. So you can't say these people just throw their disc in the water and walk off.
First day out on a course I hadn't played in forever I threw my surge low and it hit water right behind the fountain in the center of the pond... I walked to my car, grabbed a new surge out, and continued back to the hole. I then realized that the surge somehow caught an air pocket and was slowly floating to the edge of the pond. The point is, I threw it in the water, I wasn't going into the water to get it so I had already replaced it. If my disc had sunk to the bottom and I had put my number on it, do I deserve it back for free? If you call the numbers, I think you should do what someone said before. Charge a $5 finders fee, you are going in on your own time, spending your own money on equipment to go in there. You deserve some compensation, the person that threw it in there does not deserve a free disc.
edit: Risk vs Reward. Throw a floater if you don't wanna chance losing a disc.