During the Spring and Autumn period, a city gate in the State of Song suddenly caught fire. In an instant, flames raged and thick smoke billowed. Someone shouted loudly, "Disaster! The city gate is on fire! Come quickly and help put it out!"
The gate guards and nearby residents, seeing the city gate ablaze, rushed to put out the fire—some carrying buckets, others clutching bronze basins.
Beside the city gate was a moat (also called a "pool" in ancient times), the only water source nearby. People rushed to draw water from it, pouring bucket after bucket and basin after basin onto the gate. After a tense and fierce battle, the blazing fire on the gate was finally extinguished.
By then, the firefighters realized the moat had been drained dry. The river had once teemed with fish, but the great fire brought disaster upon these innocent creatures. Some fish were scooped up in buckets and thrown into the flames to fight the blaze; the rest, deprived of water, struggled in the mud—the larger ones were taken home for food, while the smaller ones perished, dried out at the bottom of the pond.
Later, the idiom "A Fire at the City Gate Brings Disaster to the Fish in the Moat" came to describe innocent people caught up in trouble and harmed; "fish in the moat" is used as a metaphor for victims unjustly implicated.
Source: *Fengsu Tongyi*
Meaning of the Idiom: Later, the Chinese idiom "城门失火，殃及池鱼" came to describe innocent people caught up in trouble and harmed; "fish in the moat" is used as a metaphor for victims unjustly implicated.