Manatees, aquatic mammals inhabiting Florida' s rivers and coastal waters, swim close to the surface and are frequently killed in collisions with boats  To address the problem, boat traffic in manatee-populated waters is being required to maintain very low speeds  Unfortunately, manatees are unable to hear low-pitched sounds and a boat' s sound lowers in pitch as the boat slows
Ttherefore, this approach may in fact make things worse rather than better
The areas where boats would have to maintain low speeds were decided partly on the basis of manatee-population estimates and partly from numbers of reported collisions between manatees and boats.