How about a River Police Challenge
Here's an idea: the River Police Challenge - create a map with complex river systems, the emphasis will be on rivers, lakes, deltas, wetlands. Since the River Police is always Watching... extra care must be taken to be geologically correct. However, including multiple or very long/large islands and other river anamolies could certainly be included.
This would be a regional map, and whatever genre or required placements of villages and towns is up to you. This is a map of rivers.