You must use more energy to swim. Lose 2 chips. You were caught by a fisherman and almost mistaken for a trout, but he throws you back. Lose 3 chips. Think of some problems you could have while swimming downstream.
Dams create pools of still or slow moving water.
Water pollution could weaken you or reduce your food supply. Irrigation and other water diversions take water from you stream and make the trip more difficult. You must swim to escape a larger fish waiting in a still pool near a dam. Lose 2 chips. You are slowed by still water near the dam.