Fishing Docks with overlapping areas of influence will negatively affect each other's productivity due to overfishing.
A Fishing Dock that is placed over a smaller river can also function as a bridge.
The amount of food collected by a Fishing Dock is directly related to how much water is within its circle of influence. Placement of a fishing dock on peninsulas in lakes, on the insides of sharp river bends, or on narrow isthmuses with water on both sides will provide higher yields.
Fishermen can only fish in empty water tiles. Buildings placed over water will reduce the yield of nearby Fishing Docks. This includes Trading Posts and Bridges, and possibly the Fishing Dock itself. A Fishing Dock is not affected by buildings on solid ground.