Narrator: People flock to the springs, to swim with the manatees and to soak in the mineral waters. But their impact on the springs is minimal. The real threat is more invisible, more insidious.

Agriculture in Florida is big business.

The seemingly limitless groundwater is constantly drawn from the aquifer for crops, lawns, and golf courses - all places which are heavily dosed with nitrate-laden fertilizers. Hundreds of millions of gallons of spring water are pumped out every day.

Much of the used water percolates back into the aquifer, carrying with it a heavy load of nitrate pollutants.

Nitrates trigger an outbreak of algae, which in turn produces toxins, creating a deadly event known as red tide. Recently, red tide killed more than three hundred manatees in just a few months.

Many manatees have scars from collisions with boats and some are killed each year.

But red tide is probably the greater threat. It could wipe out the entire population in a matter of months.

The poison of red tide can seep into the aquifer and slowly work its way through miles of underground rivers.

But so far, many of the springs still run clear.

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