when the trout start feeding heavily, the oils etc from the baitfish float to the top of the water and the trout will regurgitate some as well. Looks like an oil sheen on top of the water. It starts small, and then the current will start moving it, also making it wider. So if you see some slicks pop up, you can try to go fish back behind the origin (up current) and hope to find some hungry fish. If you are serious about wanting to get better at understanding bayfishing, please go buy the Trout Support videos and watch them often. He has a whole section on slicks. ( I bought the online versions, saved them to my computer and then downloaded them to my ipad as well). A lot of scientific stuff and lots of experienced guide info as well. Every time you watch them, you pick up something.
I don't know why, but the trout feed smells like watermelon. You will be cruising along and then bam, you smell it. Sounds odd I know, but once you get a good whiff while cruising around or wading, start looking around upwind. Probably a slick somewhere near.
Bunch of stuff on youtube about slicks. Here is one.
https://www.youtube.com/watch?v=_40qVYZF2nk