CHICAGO — Under the muddy surface of the Chicago River, a bluegill swam miles upon miles, back and forth from one end of the river system to another. Next to a quiet, unused barge slip near Bubbly Creek, another bluegill remained safely tucked away during the same two-week span earlier this summer. This kind of fish is not known for being a traveler. So the strikingly different behaviors have .
Under the muddy surface of the Chicago River, a bluegill swam miles upon miles, back and forth from one end of the river system to another. Next to a quiet, unused barge slip near Bubbly Creek, another bluegill remained safely tucked away during the same two-week span earlier this summer. This kind of fish is not known for being a traveler. So the strikingly different behaviors have intrigued .