A new, highly efficient system is being used by San Francisco and New York City to detect the presence of toxins in a city's water supply, a possible sign of a terrorist attack. They have found that the best tool for monitoring such threats are bluegills, those little fish so many catch on a lazy summer afternoon.

According to an article by the Associated Press, a small number of bluegills are kept in a tank at the bottom of a city's water treatment plant because they are highly attuned to chemical imbalances in their environment. When a disturbance is present in the water, the bluegills react against it. If the computerized system of the treatment plant detects even the slightest change in a bluegill's vital signs, it sends out an e-mail alert.

Bill Lawler, the co-founder of the corporation that makes and sells these bluegill monitoring systems, said, "Nature's given us pretty much the most powerful and reliable early warning center out there."