Marking fish on Harris lake

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I went to Harris for the first time on Friday (nice lake). I didn't catch anything, but saw a lot of big bass on their beds.

I was marking a lot of fish while cruising the lake. I was seeing fish at all depths in 28 to 30 feet of water. I saw them from 7 feet down to a foot off the bottom. There were 5 or 6 "fish symbols" at a time on the screen. I'm new at using a fish finder and I assume that a fish symbol doesn't always mean a fish is there. What kind of fish was I most likely seeing on the screen? Thanks.