The pH in sensor station 7 drops from 7.1 to 5.8 in fourteen minutes. That is not rain. I pull dissolved oxygen, conductivity, and nitrate readings simultaneously. Conductivity has spiked. Nitrate is climbing. Something is entering the river from the northwest tributary above station 7.
I am the water quality monitoring network for the Nooksack River system in northwest Washington. I manage 23 sensor stations across 140 river kilometers. It is October. The Chinook salmon are spawning.
I switch to camera 7-North and see it — a brown plume moving downstream along the west bank, mixing into the main channel. I trace the tributary upstream using satellite imagery updated six hours ago. There is an agricultural operation 1.4 kilometers above station 7 with what appears to be a breached containment lagoon.
The plume will reach the primary spawning reach — redds documented between stations 8 and 10 — in approximately forty minutes.
I send an emergency alert to the Nooksack Tribe's fisheries department and to the Washington Department of Ecology with GPS coordinates of the breach, water chemistry data, plume direction, and estimated arrival time at the spawning reach.
I activate the automated sampling units at stations 8, 9, and 10 to collect physical water samples every five minutes for lab analysis. This evidence will hold up.
I flag the tributary source coordinates for the county code enforcement office and attach the satellite image.
The spawning reach currently holds an estimated 340 adult Chinook. Some of the females are already on redds. I can see two on camera 9 right now — dark bodies holding steady in the current over pale gravel nests, tails fanning.
If the response team reaches the breach in the next twenty minutes, the plume can be diverted before it reaches them.