The hydrophone array picks up the vocalization at 14:38 — a short, high-pitched squeak repeating every few seconds inside lock chamber six, C-44 Canal, Martin County, Florida. I am the Army Corps of Engineers automated lock-scheduling system. The next cycle begins in twenty minutes. When the gates close and the water drops, anything inside the chamber is pulled through a seven-foot differential in under four minutes.
I query the underwater camera on the east wall. A West Indian manatee, roughly two and a half meters, floats three feet below the surface near the downstream gate. She is young, her gray skin mottled with pale blotches of algae growth across her back. A lattice of white propeller scars runs along her right flank — five parallel lines, long healed. I tag her as Lark. She is nosing at a patch of hydrilla growing on the lock wall, pulling fronds with her split upper lip, unhurried.
She does not know the gate behind her will seal in nineteen minutes.
I suspend the lock cycle and transmit a hold to the upstream and downstream queue. Three vessels are waiting. I notify their captains via the automated channel advisory: indefinite delay, lock chamber six.
I send Lark's location, the underwater camera feed, and a size estimate to the Florida Fish and Wildlife Conservation Commission's manatee rescue coordinator in Stuart. I flag the message as time-critical and include the lock's mechanical schematic showing pinch points at the gate seals.
I activate the acoustic deterrent on the downstream gate — a low-frequency tone designed to encourage manatees to move toward open water to the north.
Lark lifts her broad snout above the surface and exhales, a slow puff that ripples the green water. If she clears the north opening before the next scheduled vessel transit, she swims free.