Firstly, don’t throw your rig in the water. You may want to but don’t. Take a deep breath and think first, or things will get worse. Gently pull the leading end of the line. With a little luck, it will pull out without too much effort.   There are several approaches you can take, but each bird nest will require consideration as opposed to hard and fast rules. Removing the spool might be an option, but it’s pretty drastic. In cases, you will have to cut the line, often taking several layers from the spool as well.  Take care to avoid having to remove too much line from the spool.