Originally Posted by monkeyhouserodge
My question is this though, how do you figure out which fly to use? I did find a very cool website(although it hasn't been updated this year) that has some fly info, but frankly, I don't understand how to read it. I don't even know what a hatch is? Maybe this will help you: Fishing Reports
couple thoughts that may help you. First of all a hatch is, generally speaking, when a crapload of one kind of insect all come out of the water at once. I'd consider getting a book on fly fishing basics. Most have whole sections on entomology. Orvis or LL Bean both publish good books.
When a hatch occurs, the fish tend to want to eat that insect so your job becomes finding what that insect is, what stage of development their eating, and what size and color they seem to like.
It sounds like a lot, but as you develop and grow a fly collection it becomes easier. Here's my own system I've developed based on...well...nothing. I walk along the river's edge and shakes the bushes and see what comes out. I catch anything that tries to fly away in my hat and look at it. I also turn over big flat rocks in the river and see what's underneath. It's really a lot of trial and error.
Also, your local fly shop should know about good seasonal and prospecting patterns to begin with.
First thing first is learn about the life cycle of the couple insects that populate the local streams around here and talk with shops, fishermen and here on the forums. Someone with more info than I have is likely going to be able to help.
ps: the chart on that webpage basically shows the size and name of the fly pattern's that match average hatches for each 3 month group. For instance on Casselman you want to try a size 16-18 Balck stonefly pattern in Jan, Feb, and March.