Sounds like it could be a good idea. As to whether to keep the event withing the church versus going outside of the church, you might consider going outside of the church and making it an evangelistic event. Fostering inter-church relationships is important, but an outreach could have really good potential to reach youths. If you have enough avid adult fishermen in your church, you might think about inviting a local youth home or something where youths don't get a chance to get out in nature very often. I think something like that could mean a lot for both the adults and youths and it could really be a blast. As for location, I would pick a medium sized lake that everyone can enjoy, and then everyone could fish without crowding, yet everyone is still enjoying the same place. Hope these suggestions help.
Thanks for the suggestions. I have a bit of a hard time choosing a specific location to fish since I personally would want to make that choice after I know the age range and fishing experience of whoever I get paired with. For example, if I had an older youth with fishing skills I would probably choose Lake Huron for walleyes. If I had a younger novice, I would probably choose the Fletcher Floodwater where the kid could catch a 100 panfish in a very short period of time. I am extimating that we have at least 50 adults with boats that would particpate and others in the church could handle the meals and other games in the afternoon. There are also the concerns of safety and liability to consider.