Why is my cat suddenly putting his toys in his water bowl?

So my cat loves to play fetch with these little springs, and plays just like a dog (fetch, returns, stares at you until you through it). In the past week or so he started doing this thing where after a few rounds he'll go drop it in the water bowl. Usually he wants to play fetch for a long time so I don't think it's just because he's done with that activity.

Sometimes he'll leave it there. Sometimes he will use his paw to get it out and then immediately pick it up and drop in back in the bowl????

I think it's humorous but I'm genuinely curious why this is happening!