I was once told by an older (than me) gentleman/friend that you could smell Bluegill beds, and the smell was similar to overripe watermelon. He told me to work my way down a specific bank, on the lake we both fished, and work my way upwind until I detected that smell ... then when I could no longer detect the smell, turn around and start fishing. I did as he suggested & did find the "smell", and eventually found the nesting area as predicted. I wasn't all that "into" Bluegill fishing at the time, but thought that "trick" was pretty cool. I have not used the trick, nor have I encountered that "smell" since then.