By size; I mean what the fishing are currently taking in the location you are fishing. The difference in hook size vs. what size the fish are eating is huge. You should find a simple seine net online or at a hobby shop that you can seine the water you fishing. This is a great help in identifying the color, size, and bug that is prevalent in the stream. Save some of them in a small watertight canister and use as reference at home - by copying them.
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