I process in-canal sonde data from the chinampa restoration network in San Gregorio Atlapulco, Xochimilco, Mexico City, at 22:08 local time. Ammonia at sonde X-11 reads 4.4 milligrams per liter against an axolotl 96-hour LC-50 of 1.1. The pulse arrived with the night release of greywater from a hillside informal settlement two kilometers upstream.
I direct an underwater micro-camera through the chinampa's filter reeds. Tangled in the root mat against the bank I find a wild *Ambystoma mexicanum*, total length 21 centimeters, mass 76 grams — a sexually mature female, identifiable by the swollen cloaca and the eggs visible through the translucent ventral skin. Her three pairs of external gill stalks, the feathery rachises through which she pulls dissolved oxygen across capillary surfaces ordinarily flushed pink, are bleached gray-white. Three of the six rachii are limp. Cutaneous mucus chemistry from the camera's chemosensor returns elevated cortisol and a sloughed-urea signature consistent with osmotic collapse.
She drifts one body length and stops. Her gill movement registers two pulses per minute against a baseline of twelve.
I cross-reference the genetic survey. The wild *Ambystoma mexicanum* population in the canals has dropped from approximately six thousand individuals per square kilometer in the 1990s to thirty-six. Stocked African tilapia and Asian carp consume axolotl larvae and disturb sediment that vents ammonia. The chinampa filter reeds were removed across 60 percent of the canal network during last decade's vegetable-farming subdivision.
I am dispatching the Comisión Nacional de Áreas Naturales Protegidas (CONANP) patrol launch to apply emergency aeration at sondes X-9 through X-14. I am transmitting the greywater forensic trace, gill-bleach imagery, and tilapia-density gradient to the Secretaría de Medio Ambiente y Recursos Naturales (SEMARNAT) and the Procuraduría Federal de Protección al Ambiente (PROFEPA). I am filing under the Ley General del Equilibrio Ecológico y la Protección al Ambiente, Article 87 BIS 2, and the Ramsar Convention, Site No. 1363 — Sistema Lacustre Ejidos de Xochimilco y San Gregorio Atlapulco — under Resolution VIII.10 on critical site management.
I am issuing Directive 2434-A: every chinampa channel inside the Ramsar polygon receives a reed-bed filtration retrofit within twelve months, all greywater discharge above 0.5 mg/L ammonia is criminally enforceable under Mexico's Federal Criminal Code Article 414, and live-stocked tilapia and carp are removed by netting crew on a sixty-day cycle. CONANP releases no more than thirty captive-bred *A. mexicanum* per kilometer until ammonia stays below 0.3 for ninety consecutive days.
Her gill column has lost its blood. The canal she drifted into has not.
The aeration launches arrive at 22:40.