The US has responded to the possible threat of terror attack against its drinking water supplies by using fish to monitor the state of the H₂O, the BBC reports.

New York, San Francisco and Washington now boast tanks containing small numbers of bluegills, aka sunfish, into which muncipal water is constantly pumped. A computer system "registers changes in the fishes' vital signs" and when something is amiss sends an alert via email, pager, or "fish phone" mobile device.

Bill Lawler, co-founder of San Diego-based Intelligent Automation Corporation, which makes the "Intelligent Aquatic BioMonitoring System", said: "It's like an early warning system - it acts as another line of defence."

The New York blugill terror vigilantes have already earned their keep - they recently detected a diesel spill in the water supply before any of the Department of Environmental Protection's other monitoring equipment sprang into action.

They do, however, have their limitations. The BBC rather brilliantly notes they "cannot reliably detect germs and are no use against other sorts of attacks - the bombing of a water main, or computer hackers attacking the systems that control the flow of water". ®

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